The best thing to do is schedule your day and at least know when important dates are.
Study in the library, outside, or anywhere where you won't have distractions. At my house I have high speed internet, multitudes of books, and a multutide of things that can draw my attention away from working; you have to be able to focus on what you are doing. It is best to work in study groups with people from your classes or else some subjects will just bog you down because they are so tiring. Go to the office hours of your professors and TAs because they will be able to help you much more there than in a classroom setting (usually).
Eat right even though you will most likely be poor. A pizza a night with Ramon Noodles is not healthy. It will just make you gain weight, feel lathargic, and can easily destroy your confidence. Wake up early and exercise in the morning if you can (just a personal preference for me). Sleeping in until noon works for some people, but it makes me think just how much of the day I wasted.
Last, try to enjoy the time you do have off. Make friends and don't party too hard. Even if you spend most of your time hanging out out with the same people in your classes doing work, at least get to know them well. However, girlfriends and lovers tend to take plenty of time and money which you won't have. They can be great, but usually you put off or slack off quite a bit because of them. On the other side, there are a ton of people here who go to class, study, sleep, and then do it all over again without ever really interacting with anyone.
Last, just remind yourself that only 25% of incoming freshmen will graduate with a degree. Most waste the oppurtunity they have with excess and laziness. You have to be able to balance it.