Writing Effective Songs/Solid "Praise & Worship" songs
It doesn't matter if the song is gospel, hymns, spirituals, soul, and etc., they are all "Praise and Worship" songs dedicated to God. In order to write a song ascribing the worth that is due God, we must first find out what He is worth. In order to even attempt to describe God, we must know Him more and more.
Just because one is a non-Christian does not mean they should stay away from understanding it, since many American Musics - be they Blues or Jazz - was deeply rooted in the call-and-response of Spirituals. Additionally, it is quite imparative to study this unique music genre, to see what makes the music powerful to sway a large crowd.
Here are a few important aspect to writing a Praise and Worship song:
Heart of submission 
- You need a heart that is full of the Glory of God
- From the overflow of the heart, the mouth speaks. Word of God in . . . Word of God out. Strive to expand your worship vocabulary. Yes, "Praise the Lord!" is a wonderful expression, but God is so much bigger than that. If you're going to write about things spiritual, the most important thing is to keep your spiritual life going. Your writing becomes dry when your spiritual life is dry.
- Was it a prompting from the Holy Spirit? - Pray for further direction. Seek Him to help you finish it. Sing Scripture to it - if you have a favorite, try it (e.g., "Psalm 119").
- Sing your testimony to it.
- Sing a prayer to God to it. (e.g., In the Quiet).
Choice of words 
- Scripture - more of "The Word" in the words
- When scripture is married to music ("the one expression that God created that bypasses the intellect"), it drives straight into the heart of the listener and deposits that word or seed there, which WILL NOT - according to His own promise – return void. Have you ever noticed it's easier to memorize scripture that has been set to music? Praise songs that contain The Word feed the heart in preparation for the worship time.
- Lyrics that declare His attributes (i.e. our Healer, our Provider, our Peace etc.), for He brings those attributes to bear on our present circumstance as we sing them.
- Lyrics that declare an awareness of and response to the glory and sovereignty of God.
- Call-and-response is a very effective way to get in touch with the Holy spirit, for both the audience and the musician him/herself
- The most powerful imagery in a Praise and Worship Song is imagery that points people to God.
- Just plain, does it minister?
- Is it prophetic or evangelistic?
- Does it create an atmosphere for praise or worship?
Performance and outcome 
- Has the Holy Spirit been produced right out of the song?
- Has it gone right over the common person's head?
- Can it be played with any instruments, be it keyboard, acoustic guitar, electric guitar, flute, djembe— be it a combination, individual, or even acapella?
- The Names of The Lord - Proclaiming one of the many names of the Lord and their meanings
- Gods Love - The depth and breadth
- Healing - Calling upon the Lord for physical or spiritual or emotional healing
- Holiness - Seeking sanctification and purity
- Surrender - Laying down our wills to be replaced by His
- Declaration - Affirming who God is in our lives
- Exaltation - High praise, praise with abandon to self consciousness
- Exhortation - Encouraging the assembly
- Spiritual Warfare - Is it a rally or battle cry?
- Focused mainly on God
- Focused mainly on Jesus
- Focused mainly on the Holy Spirit
- Repentance - Confession and asking for forgiveness
- Thankfulness - Gratitude for Who He is, and all He's done
- Adoration - Lavishing our deepest love upon Him
Ways to increase the spirtual creativity 
- Bible study
- Sermons - Something as simple as a single phrase (e.g., "High King of Heaven")
- Sermon topics
- Fasting - Marty Nystrom wrote "As The Deer Panteth For The Water" on the 19th day of an extended fast. As we put the flesh under and deny it, the spirit man rises up and becomes more receptive (e.g., "Lord of Lords").
And finally . . . and most importantly . . .if you want to be truly used of God in a powerful way through your songwriting, then give your heart TOTALLY to Christ and give that gift to God.