Strategy Basics 
You may choose different strategies depending on what type of opponent you are playing, and what kind of player you are. Strategy starts with the opening, and continues through the middlegame, and on to the endgame.
Games are considered open if the exchange of pieces have opened up files or diagonals, and closed if they have not. These games are called open or closed because there is more mobility for one’s pieces in open games, and usually determine the complexity of the game. Specifically, recognition of open versus closed games is important because closed games are more conducive to Knights, whereas open games see more involvement with longer range pieces such as Bishops, Queens, and Rooks.
Strategic Openings: If you choose to play a long-range, theoretical sort of game, you may want to choose a complex opening such as the Queen’s Gambit, the Ruy Lopez, or the English. In these types of games, especially when you are playing the closed variations, you are likely to venture into close positions where positional maneuvering predominates over tactical shots. From there, you can focus on strategic elements like controlling files, pawn structure, and other long range development considerations.
Tactical Openings: If you are more interested in sharpening your tactical play and focusing on combinations, you may choose a more tactical opening. Some of these openings include the Sicilian Defence (especially the Dragon and the old main line of the Najdorf), the Grünfeld Defence, and the older variations of the Two Knights' Defence.
By initiating exchanges you can always simplify the game, and it will become more computational. If you don’t want that to happen, you have to be very guarded and conservative.
You should always be thinking about how many squares a piece controls (i.e. can attack), and which squares are controlled. In the beginning you should aim to control the center of the board. As the game progresses you may want to attack one flank, especially if the King has castled onto that side.
Material advantage 
Having more valuable pieces on the board than your opponent means you have a material advantage. If your position otherwise is equal, you will be more likely to win. Since not all pieces are equal, many people use the following point system to estimate which player has a greater material advantage:
- Pawn = 1
- Knight = 3
- Bishop = 3
- Rook = 5
- Queen = 9
- King = infinite (3.5 as an attack/defense strength during end game)
However, a slightly more accurate system is as follows:
- Pawn = 1
- Knight = 3½
- Bishop = 3½
- Rook = 5
- Queen = 9
- King = infinite
These values can only be used as guidelines for the relative value of the pieces; a piece's value in a particular chess position must be treated on a case-by-case basis.
Queenside vs Kingside 
When calculating the value of a position, dividing the board in Queenside and Kingside, it will be seen that it matters that the king is considered to be worth 3.5 points. The calculation of forces on either side will determine the stronger side. This side, usually can become the attacking one, all other things considered.1
The pieces' relative value changes over time 
The value of the pieces changes as the game progresses, because there is less material on the board to get in the way of some pieces. Rooks usually become more powerful because there are fewer pawns in the way, and a rook has the opportunity to control more squares. Bishops can travel great distances if unobstructed, while knights have a more local presence. So, knights shine when the board is cluttered in a closed game because they can "jump" over pieces whereas bishops are generally stronger in open games where they have the run of the board.
The value of the King 
Assigning a point value to the King for the sake of deciding to trade the King for other pieces doesn’t make sense, since capturing the King is the object of the entire game! Therefore it is customary to either exclude the King from the point value scale, or assign it an infinite value. However, keep in mind that the King has an attacking and defense capability as any other piece.
The King attack and defense value changes dramatically as the game progresses. During the opening and middle game the King is a piece that needs to be protected against checkmate at all cost. Its usefulness as an attacking or defending piece is thus limited. However its strength as an attacking piece becomes greater in the endgame. In this phase of the game it is generally reckoned to be stronger than a knight or bishop but weaker than a rook. Therefore giving the King an attack or defense point value of 3.5 during the endgame makes sense.
Knight vs Bishop 
Based on the point value scale above the value of the Knight and Bishop appears to be the same. Alternative scales have tried to assign the Knight and the Bishop slightly different values, usually preferring the Bishop over the Knight. But since the relative value of the Knight and Bishop is strongly related to the position, such minor differentiation provide little overall guidance.
Knights are more powerful if they have a safe outpost in enemy territory - a knight on the 6th rank that can not be attacked by opposing pawns can be as powerful as a rook in the right circumstances. This type of knight, if guarded by a pawn, is called “a home away from home”.
A bishop never leaves its own color, so if one of the bishops is captured, half the board is now out of reach of a bishop. So trading one bishop for a knight tends to favor the person losing the knight, who is left with two bishops. However, trading the second bishop isn't quite so hurtful. So trading a Bishop for a Bishop where one side has only 1 bishop to begin with helps the side with fewer bishops.
Knights can not cover both sides of the board at the same time, while a bishop can, so in an endgame where there are pawns on both sides of the board, the bishop is stronger.
Bishops can not attack pawns that are on the opposite color, while a knight can. Furthermore, in a game where there is a short pawn chain, a knight can stand at the head of the chain and attack the pawn supporting it, so a knight is often more effective attacking pawns as long as they are limited to one side of the board.
Finally, it is possible to force checkmate with two bishops and king against a lone king, but not with two knights and king versus lone king.
It is important to keep in mind what sorts of positions will benefit the pieces that you have. For example if you have 2 knights and no bishops and your opponent has 2 bishops and no knights then it would be good for you to keep the center cluttered with pawns by avoiding pawn exchanges. If you do this then your opponent's bishops will have hampered mobility whereas your knights can hop over the pawns. Also if you have the bishops and your opponent has knights then you should play to keep the center clear so your bishops can have more mobility. Also, this idea can help you decide on whether or not to trade a bishop for a knight or vice versa.
More pieces are usually better 
Usually having more pieces are more valuable when the point value is roughly equal for both players -- two bishops beats a rook, two rooks beat a queen -- but this is conditioned on proper co-ordination between the pieces. It may be worthwhile to sacrifice two pieces for a rook if this results in long-term damage to the enemy's piece co-ordination. Usually this means tying down the extra pieces to the defense of weak pawns, so that they cannot cooperate in attacking friendly pawns.
Material values only matter in the context of position. Compensation is a term used in chess to describe the trade off between material and positional advantage. A strong position can make up for a material deficiency. For example if your opponent has all their pawns on white squares, a black bishop is worth more than a white bishop.
Typically having compensation for a piece means that an attack against the enemy's king or strong points cannot be repelled or may only be repelled by the enemy returning the material he is up. Often compensation can refer to having the initiative or in trapping the opponents king in a vulnerable position. A pawn majority on one wing or a passed pawn can also sometimes be considered compensation for a minor piece. Generally the player who is down on material has to act quickly and avoid exchanging pieces to prevent the enemy from making his material advantage count.
Pawn Strategy and Pawn Chains 
In the end game, pawns gain strength as they advance because they pose the threat of promotion, so a pawn on the 6th or 7th rank is worth significantly more than a pawn on the second rank - often as much as a piece. However, in the opening and middlegame, an advanced pawn is less likely to queen and more likely to be in need of being defended. It is also unable to defend the center and often leaves "holes" in your territory that can serve as outposts for your opponent's pieces. An overadvanced pawn is then often a liability.
In the opening and middle game, pawns in the center of the board block paths and support outposts. So they tend to be more valuable than end pawns. However, in the end game, a wing pawn is usually the hardest to get to and block or capture and is therefore more likely to queen. So in the endgame, the edge pawns are often more valuable than the middle pawns (Note: this is not necessarily true in some basic pawn and king endings, where a pawn on the edge leads to only drawing options).
A passed pawn has only pieces stopping it from queening, so it is considered more valuable - especially if it is protected with other pawns.
Tempo is the effective number of moves required to reach the position on the board. Moving a piece twice to reach a position it could have reached in one results in a net loss of one tempo - moving a piece back to its starting place usually results in a loss of all its tempo - unless other pieces moved that could not have moved otherwise. Also the capture of a piece means all of the tempo it gained is lost as well.
Essentially, tempo is one way of showing how many effective moves you have made. So the gain of a tempo is basically like getting a move for free. Three tempi is usually considered equivalent to a pawn in terms of advantage.
In the position above there have been 2 tempi played on each side, play continues with:
3. cxd5 Nxd5 4. e4 Nf6
Now white still has 2 Tempi (one for d4 and 1 for e4) while black only has 1. The captured pieces lost the tempo they had gained in moving and the knight lost the tempo it had when it captured.
For argument's sake, lets assume play went as follows:
5. e5 Nd5 6. Bc4 Nb6 7. Qd3 Na4 8. Nc3 Nxc3 9. Qxc3 e6
Now black still has only 1 tempo (e6) while white has 6 (2 queen moves, 3 pawn moves and a bishop move). This has let white develop 2 pieces, control the center and give black a cramped position. Also, while both sides can castle kingside in the same number of moves, White can connect his rooks (position them so there is nothing between them on the back rank) 2 moves sooner than black. Chances are, white will complete development and launch an attack before black is able to. This means white will have an advantage when the middlegame is reached.
Active and passive pieces 
An active piece is one that has the potential to make a threat. A passive one is usually relegated to defending a piece (or worse - a pawn).
In this example, white's bishop on g5 is considered active, while black's bishop on e7 is considered passive.
Piece activity depends on whether it can move and attack. A piece can be rendered passive if it is stuck protecting another piece or if it is restricted from being able to get into play by its own pawns.
Good vs. Bad Bishops 
As noted above, a bishop can only travel on squares of one color. This leads to a situation wherein one bishop may be effectively blocked out of the game by the pawn structure. In general it is better to have your pawns on the opposite colored squares to your bishop. For example, if you as black have pawns on e6 and d5, your queen's bishop is likely to be a "bad bishop." It is bad because it is hard to do anything constructive with it; developing it to g4 is impossible and "fianchettoing" it via b7 is ineffective since your pawn on d5 blocks any influence it may have over the centre.
When one has a bad bishop there are two methods to improve the game: exchanging the offender and freeing up the game. In general it is profitable to try to exchange your bad bishop for an opponent's bishop or knight, as your bad bishop has little value. However, it is important to bear in mind that in the end game having two bishops is considerably stronger than have two knights or a bishop and a knight. Therefore you should always be wary of exchanging bishop for knight in situations where an endgame is likely. The other method to rid yourself of this weakness is by freeing up the game through making pawn moves.
Overloaded pieces 
Overloaded pieces are pieces which defend too many other pieces and therefore cannot be considered to defend all of them at once. For example, a rook can defend up to 4 pieces, but if one is taken, and the rook takes the offending piece, 2 of the other pieces are undefended.
The player with the initiative is the player who is making the threats to which the other person must respond. Having the initiative is advantageous because it forces your opponent to place his pieces in essentially defensive formations. A piece that is defending a square generally has less mobility (freedom of movement) than a piece attacking the same square.
Having the first move, it is generally white who has the initiative in the early part of the game. Therefore trying to maintain the initiative would be prudent strategy.
A Zugzwang situation occurs when any move a player makes will weaken his/her position, but he/she is compelled to move in accordance with the rules. An example of the zugzwang is as follows:
White moves and wins.
1. a4 : White moves the a-pawn, blocking the black a-pawn to move forward. Black has only one legal move; moving the black king out of the way of the d-pawns path.
1. ... Ke7 : The black king is forced to move away from his current position where he blocks the d-pawns path to promotion, because he now has no other legal move to make. Since this move is not desired by Black, he rather wish to keep his king on the d8 square where it stands to continue blocking the white d-pawn, the move is zugzwang (forced).
2. Kc7 : White's king continue to protect the pawn on d7 from capture, and blocks black's king to move back to it desired location of d8.
2. ... Ke6 : Black can make other legal moves with the black king, but they will yield the same result. Even if Black must move the king, this is not an example of zugzwang. Keeping the king at e7 would not yield a better result for Black, since the d8 promotion square is protected by the white king.
3. d8Q : White gains a queen and wins the game easily.
Exercise: From the same initial position but with black to move first, show that Black can force a draw by using zugzwang.
Solution: 1. ... a4 2. Kb5 Kxd7 (White's move is Zugzwang.) 3. Kxa4 Kc7 4. Kb5 Kb7 5. a4 Ka7 6. a5 Ka8 7. Kb6 Kb8 8. a6 Ka8 9. a7 (Draw by stalemate.)
Combining attack with defense 
A winning strategy in Chess often involves balancing several considerations against each other. Moves that maximize immediate material gain might expose a vulnerability or yield a difficult position as the game progresses. Similarly, material sacrifices for position may be disadvantageous if they cannot be parlayed into an effective attack. Thus, a key consideration should be balancing attack with defense. A profitable move would be one that both furthers your attack and solidifies your defense.
- ^1 Yasser Seirawan in his Pro Mentor DVD.