This is where I start whenever I'm trying to put a setlist together: PRAYER and waiting on The Lord.
Proverbs 3:5,6 NKJV "Trust in the Lord with all your heart, and lean not on your own understanding. In all your ways acknowledge Him, and He shall direct your paths."
I like The Living Bible version: "If you want favor with both God and man, and a reputation for good judgement and common sense, then trust the Lord completely; don't ever trust yourself. In everything you do, put God first, and He will direct you and crown your efforts with success."
You can do all the research, all the work, all the practicing; basically do everything on your own and YOU get all the glory. Or, you can acknowledge to Him that you're not too sure of yourself, and that you need His help and guidance, and watch Him take your work to a whole nutha level, so HIS name will be glorified.
Pray together with your HS student before you get down to business for the day, you pray first and then let her pray and express what's in her heart. Sometimes, when students pray they open up a lot more than when they're just talking. Then you'll be able to gauge a little better where she/he is at on that day. Pray that He will guide you as you listen to klove or "research" songs. Pray that certain words or phrases will jump out at you as you thumb through your songbooks. Tell Him that you're doing this all for HIS glory, not YOURS, and when you hear His voice guiding you don't second guess Him, go with your first "gut instinct" and you'll be amazed at how your song selection will just "somehow" flow.
Mark