The opening is the time when a power chooses its tack towards its first few centers. During the first few turns, a wise player aims for neutral supply centers in order to bolster his forces for the coming wars.
At the beginning of the game, each country has moderately consistent goals as to which neutral supply centers to target. Some supply centers are almost guaranteed to certain nations, others are based more on individual diplomacy and tactics.
If Russia is not hostile, England can easily take Norway before the first build. Besides that England will also target Holland and Belgium, either working with France or Germany to land his army on one or the other.
Spain is almost always captured by France. The taking of Portugal is sometimes delayed until after the first build due to troop requirements elsewhere. France, like England and Germany, also has a stake in taking Belgium.
Germany can take either Denmark or Holland, but is not guaranteed both. A hostile England can block Germany from a second supply center in the north. Germany also has the option of blocking Russia out of Sweden before the first build.
Despite being the largest starting power on the map, no supply centers are guaranteed to Russia before the first build. Moving to Rumania is difficult due to the need to protect the Black Sea, and while Sweden can usually be secured, a hostile Germany can bounce Russia out with the right opener.
Italy will usually make a grab for the safe Tunis, but a more aggressive or risk-loving Italian will gun for Greece with the support of Austria or Turkey. As it stands, it is almost impossible for Italy to grab 2 supply centers before the first build, short of brutally assaulting Trieste (if he hates Austria).
Austria is often concerned more for maintaining safety and stability than grabbing supply centers, but Serbia is often a given and conflicts between Trieste and Venice can sometimes lead to a supply center, or a lack of one, for Austria.
Bulgaria is a given for Turkey, and through good diplomacy and a fast rush, Sevastopol or Greece sometimes become available.
Safety is especially important for powers that can be eliminated or crippled early--Austria, Russia, Germany, and Italy. With Austria, Russia, and Turkey all sharing a stake in the Balkans, the mutual mistrust generated by the three countries' relative instability can turn into a three-way war in which the strongest tactician, or more often, the luckiest, can only hope to achieve moderate success.
England is in another situation entirely. They are quite safe in the beginning because both France and Germany need to first build up their fleets before they can consider invading England. However, the danger lies in a lack of expansion: if England cannot secure enough territories fast, they will simply be holed up on their island.
Turkey, despite being in an unstable area is rarely eliminated in the opening, simply because they have a strong defensive position. Italy usually will either move west towards France or surprise attack Austria, while Russia has too many fronts to focus on to really threaten Turkey. Turkey tends to lose due to their slow rate of expansion, the exception being if Austria and Italy really work together with everything they have to eliminate Turkey. If this occurs Turkey may end up being "stuffed."
The least safe of the starting countries are Germany and Austria because they are in the middle of the board and can be threatened from all angles. Both Austria and Germany must expand fast to make up for this disadvantage.
After considering safety, growth should be an important factor. How quickly are you expanding? Expanding too slowly will hurt when a strong power decides to hit you later on. Rapid growth is important to beef up your power's territory. However, building up too fast could mean an alliance between all other powers to bring you down before you overpower them; because of that, a player should try to always provide a bigger threat to his potential enemies. For instance, a strong England in the early stages of the game might want to point out to Germany that Russia is also very strong and if Germany attacks England, they will be weak on the eastern flank.
Movement to the Middle Game
After all neutral supply centers have been seized by one power or another then the board moves officially into the middle game.