It is hard to pray for someone you do not know enough. The following acrostic is a suggested way of praying for a person.
Faith is the subtance of things hoped for and the evidence of things unseeen - Heb 11:1
Faith: Pray for the salvation of the person you are interceding for. Pray that the person may come to a saving knowledge of Jesus Christ.
Answers to prayer: Pray that the person's prayers be answered.
Idols: Pray that the person's idols be demolished. A nice way to identify idols is by identifying what IDOLove.
Trials: Pray for the person's deliverance from trials that the person is currently going through.
Health: Pray for the physical health of the person.