Make sure you've got binders or folders for every class. If you've got a laptop, which is highly recommended, create desktop folders for each of your classes so you can keep track of assignments, papers, labs and readings. Depending on your course of study, you might have hundreds of pages of reading and dozens of assignments and supplemental materials at any one time. It's crucial that you can access all of your materials quickly and easily. Keep a calendar on you at all times, whether it's on your computer, cell phone or in paper form. Keep track of each of your short- and long-term assignments each day. Separate your academic, extra-curricular and social obligations by color-coding so you can prioritize if necessary.
As tempting as it may be to sleep until noon on the Tuesdays and Thursdays where you've only got an oceanography discussion, resist the urge. There's nothing wrong with taking advantage of your opportunities to catch some extra sleep, but the studying and busywork you don't get done in the free mornings or early afternoons you've got now will translate into miserable and sleepless (and fun-free nights) down the road, when you need to focus on studying for finals. Get the studying for your most difficult subjects out of the way first. This way, if you're struggling, you've got plenty of time to get extra help and make sure you do well in the class. Keep up with reading, and take advantage of reading and writing centers on campus that can help you learn how to read smarter. If your reading assignments seem impossibly large, commit to learning how to identify what you need to be getting out of your reading. If you find yourself getting through your reading easily, read ahead and save some time for studying (or partying) later.
Because there is less regular homework and less accountability in terms of classroom attendance, it's easy for college students to get so far behind that they have extreme difficulty getting back on track. However, students who take no time for fun or social activities end up with high stress levels that sometimes translate to academic troubles. The key to success and mental health is finding a balance between your social life and your academic responsibilities. You will get as much or as little out of your college experience as you put in, but staying organized and keeping yourself busy are easy keys to success.