1) Psalm 20 - Seeking God's help
Psalm 20 reminds us that God is our helper in the day of trouble. As we face any battle, our trust should not be in our strength and resources, but in the Lord. Psalm 20 also tells us the end of those who trust in themselves.
2) Psalm 51 and 32 - Confession of sins and getting rid of guilt
When David had sinned grievously against God, He repented and cried out to God for forgiveness. Psalm 51 is a confession prayer and Psalm 32 helps us overcome the guilt of sin.
3) Psalm 25, 61, 86, 28,143 - Crying out to God in times of trouble
Most Psalms reflect a honest outpouring of difficult human emotions to a known God. These Psalms can be used pour out our hearts to God, even when it is hard to find words to pray.
4) Psalm 100, 150 - Praising and rejoicing in God
David praised God at all times. Most Psalms that starts with a honest plea for help in the time of distress, yet ends with praise. Praise Him, at all times.
5) Psalm 91 - Refuge in God
Is there any safe place better than the shadow of the Almighty? Where do we find our shelter and refuge? Is it a job, bank balance, relationships etc. or God?
6) Psalm 124. 126 - Remembering God's mercies
If God has not been on our side, we would have perished for eternity. It is easy to forget all the benefits we received from God and focus on what we think we lack. It is important to remind ourselves of God's mercies and answered prayers often. It is wise to write down all the answered prayers that you remember and thank God for it.