1.If you going for first time dont think your self as very experienced teacher, it may prevent to mingle with real class room atmosphere.
2.Try to be friendly with children.
3.Tell lot of jokes, if you dont know prepare it.
4.If a child like the teacher obviously the child will study well.
5.Make feel the child school is the most happiest place to get everything like friends,games,competion in reading and writing skills.
6.It is your responsibilty that child should decide that school is the only place where i can prove all my talents.Other places or not suitalble for that.This is your real challenge.