The Birth Partner by Penny Simkin is a great introduction to helping a woman in labor, and it's an easy read. Try doing some searches in this forum for threads where doulas and midwives talk about their favorite tricks, etc. You might also want to check out Ina May's Guide to Childbirth, especially the birth stories, to get you in a happy birthing frame of mind.
In my experience (though I'm still a pretty new doula), just being there, completely present and supportive, is a huge part of being a good birth partner. Also make sure that everyone has employment -- i.e. if dad's getting freaked or joking around, start giving orders and keep him busy! Protect the birth space -- be vigilant in maintaining her privacy, keep the lights low, project positivity to everyone who enters the room ("Isn't she doing a great job?!")
Good luck! Your friend is lucky to have you on her team.