Tips on this mini-party? Please Read!?

Ok, so me, my girlfriend of 6 months, my best friend (dude), and possibly 1-3 of my girlfriends best friends are coming over to my house for a 4th of July type small party. There will be swimming, volleyball/badminton, soccer, fouseball/airhocky/pingpong/billiards. We won't do all of those things but the point is we have several things to do. Any tips for this type of event? This is the first time my girlfriend will be at my house, and the first time i've held a "party" Once it gets dark we're all going to see fireworks (where me and my girl are supposed to have some decent alone time). I need to know any cautions of inviting a girlfriend to my house. We're all 15 ish. My parents like my girlfriend and she likes them, my best friend is very sociable etc. There will be food (burgers hotdogs etc). Any ideas on how to make this a great time? I realize the questions here are kinda spread out, but I'm rushing. THANKS! :D