Sandy-
It would be a really good idea to make sure you know what dances your dad is comfortable with. If he is an experienced dancer, then I would advise the "slow" waltz (slow vs Viennese, which is fast). All male dancers are told that our job is to make the woman look good, and I think that is easiest for the leader to do (especially with an inexperienced partner) with the waltz.
Good luck, and remember, mistakes dont count! The goal is to have FUN!!!
Jerry