EDIT!
Lourdes is so right! Never take a class that starts before 9am! Ever! Also, try to schedule all math and science courses for the afternoon.
I wish someone had told me to join or create study groups while in college. A great study group can make all the dfference in a difficult class!
I wish I would have joined a few clubs and organizations while in school. Not the drunken, crazy ones, but the ones that were pertinent to my major.
I wish I wouldn't have bought ANY new books. Always buy books at half.com or ecampusbooks.com or find someone who took the class the previous semester. Rent books you'll never have to use again, and buy books which require more than one semester of use. For humanities courses (like philosophy or sociology) don't buy ANY books before the class starts. Wait until you have the syllabus in hand and only buy what the instructor says you HAVE to have. For sciences and math, buy the book before the class starts, but be CERTAIN you have the right one.
If I could go back now I would study harder and SMARTER. Use the great tools available out there. If you need flash cards, you can find great flash card programs free online. Math, science, language help? Also available free online (sparknotes.com).
Why didn't someone tell me to BUY A BIKE! It's so nice to run around campus on a nice, comfy bike. And parking is MUCH easier if you can hop on a bike and park it right outside the building instead of searching for a spot.
Also, have an alarm clock that wakes you with unique noises (like chimes or other more natural sounding noises) because regular alarm clocks SUCK! And get plenty of sleep. Keep up with the reading and you'll never have to cram.
Good luck!