Use social events as a reward for getting your schoolwork done. And stick to it: if you haven't gotten your work done for the day -- no going out! You'll be amazed how productive you can become :)
Try and do you homework as soon as you get in on an evening. Spend an hour doing it have your tea and then go out!
If you don't let it build up you will have more time to go out! If you let it build up you're likely ti find a big party crops up before its all due or you will end up doing it at the weekend when you could be going out!
Prioritize! School is very important - make sure you are keeping your grades where you'd like them to be, not just what's acceptable. Plan ahead for big events by trading nights - stay in during the week to free up your weekends, and vice versa. Make time for the really important social events and put the mediocre items on the back burner.
Study and Play.
Spend half the week studying, half the week playing.simple. arrange it so its even and you'll see a difference in both sides of your life.
do any homework when you get it, dont allow it to build up. put social events in your calendar as an incentive to keep up to date with work so it does not spoil the event.