Emily Post = she has a Q&A section on the Net
Debrett's = might give you what you're looking for. However, I could not find anything specific for Prom
Moyra Bremner = Modern Manners
My suggestion:
Walk ladylike (never rush, or run)
Sit ladylike (don't cross your legs)
Drink your drink like a lady (sip it, and hold the glass in one hand).
Speak like a lady (not loud, but audible)
The key word is >>> Discretion ... don't make a show.
Dress discretely.
Wear a long dress and pumps (1.5"-2" heels), and a little evening purse.
If your hair is long, wear it up. It makes you look taller and more elegant.
Most of all .... relax
Have fun
".."