Kegs - First thing, you need kegs. Get an idea of how many people are coming and what type of drinkers they are. If you have a bunch of girls, then you'll need less kegs. I would 1 keg for every 15-20 people. You will also need a tap, a bucket and solo cups. The package store should supply you with those.
Step2
Games - Games are necessary. Set up a beer pong (beirut) table for sure. Google if you don't know what that is. Also set up a table to play cards.
Step3
Music - Get some upbeat music going, preferably hip hop or pop.
Step4
Food - Don't overdo it on the food, all you need is some snacks. If it is a day party, you can grill up some dogs and burgers.