Honestly, uni is just about being organised and understanding your limits. Plan out your week - write up realistic figures for how much time you'll need to spend on any given subject, and work out also how long you'll need for co-curricular/social activities, etc. Having an organizer is immensely helpful, and if you're anything like me, it might get to the point where you pretty much can't live without one.
On another note, I would half agree with and also qualify TT's statement. Doing well in uni means hard work, whether it is cramming or (more advisably) a consistent approach throughout a the semester. With that said, you definitely don't have to give up all of your social life. Instead, I would appeal to the old maxim about uni - study, socialise, sleep, pick two of the three, and you're set. I've always been relatively big on sleeping (even in year twelve, I would almost always get at least seven hours), and at uni it's not uncommon for me at all to pull all-nighters or near-sleepless nights.