Lol "Today, us kids...and money." As if things have changed, ever!
To be honest, I'm not sure I'm the best to give advice...I got nowhere, as it were. However, I had a good time. I had a good time by just letting loose, and dancing and enjoying time with friends and the girl.
However, beyond just making sure to have fun, I'll go with pa; don't be disrespectful. You have the advantaged of having a girlfriend already, don't mess that up by doing anything stupid during or after.
Also, I again agree with pa, don't go for flash. A good, black tux is the perfect formal clothing for a man. It's classy. It looks good. And it never goes outta style.
My tradition, from my junior and senior proms: Denny's after the dance. With the group...none of the group was concerned with EXTRACURRICULAR ACTIVITIES, however.
Also, look up the Hitler dance. It's a Whitest Kids You Know sketch. Quite funny...and if you get a few friends to join in, it will cause a laugh. At least, did for ME and MINE lol.