I hosted one the weekend just gone man. It can be stressful because you want to make sure others are having a good time and also look after your place. My 18th was average because i spent my night worrying about others most of the night. Although you want to keep and eye on things, you need to have fun man, so let your hair down and enjoy it.
If there are girls coming you're keen on remember for the night you're the man it's your party and your social proof will be through the roof so you should find it quite easy to close. During the party I took one of the girls to the rear balcony and after talking for a bit started hooking up, in the end she was the last to leave the party!
Hope it's a good one!