Psalm 5 - When I was a teenager and really beginning to grow in my relationship with the Lord, this was one of my favorite Psalms. I especially enjoyed verse 3 about spending time with God early in the morning. I knew I needed God's guidance before any day really started. It's a habit I still practice today and trust you will find it helpful too.
Psalm 38 - This Psalm is a real help when you feel you've "blown it" and think you ruined your life, or at least you feel you ruined a good relationship; a chance for a better job; or any number of other great things that might have happened. God knows what we've done and He is the Master of forgiveness and giving second, or twenty-second, chances to restart!
Psalm 41 - When you have the opportunity to help others in need, do so. God is pleased with those who put the needs of others above their own. And when other people don't reciprocate, when those you help don't help you, don't worry about that. Your ultimate Friend is Jesus and He will uphold you because He "...sets you before His face forever" verse 12.
Psalm 42 - Most Christians have learned something about deer from this Psalm. They crave a cool drink when they're weary. And that's just what we need when we're spiritually dry. Jesus had promised living water that would be there to constantly refresh His children in their weariness. This Psalm is filled with hope and even reminds us of "songs" in the night, verse 8.