Probably too late but here it is (the ground rules may differ in various places and this is VERY US centric)
1. Take EXACTLY 15 credits. You need 12 to be full time and you need to be full time to keep your financial aid. Taking 15 leaves room to drop one course. Berzerk professors are a risk, high school was a lot easier, the competition is harder, so you need to leave room to drop one. Your college is a new place with new rules. You don't want to be learning the rules with a 24/7 load.
2. Professors are called Prof. Rabett or Dr. Rabett, not Mr. Rabett, and unless they specifically tell you to do so, never Eli. Most teaching assistants are graduate students. They should be addressed as Mr. or Ms. Adjuncts can hold the doctorate or not. Check and address them appropriately. This is college, the ground rules are different.
3. Someone told you to look your professor's in the eye, stick out your hand and say, "I'm Mr. Bunny", so they will remember you. Someone told you wrong, this doesn't even work for salesguys. Most academics are introverts, they hate this crap.
3a. OTOH when you talk to your professor the first couple of times, say "Hi, I'm Ms. Bunny and. . . ." or if you encounter your professor outside the class "I'm Ms. Bunny and I'm in your 3PM lecture class. . . "
4. There are important differences between secondary school and college. In secondary school the burden of your learning is on the teacher, if you are "not getting it" the teacher is obligated to work with you until you do. In secondary school the teacher follows a syllabus that is mandated locally, often statewide. In college, the burden of your learning is on you. The professors present the material (hopefully clearly, tho not always) on a level that they decide is appropriate for the course. (Google helicopter parents for more)
5. Get a study group for each course. The group should be no less than 4 and no more than 5 students so that if one person can't make it you still have a group and no one can hide. Meet at least once a week. Have an agenda about what you will do/discuss. You should have read the materials and at least tried to do the assigned problems. That way you can spend time on the points/problems that gave most of you trouble. If all the points/problems give everyone trouble, you have the wrong study group.
6. You want to develop a professional relationship with your professors. This means talking to them about the subject. In particular, you will get extremely short shrift if you go up to them and say something like: "I don't understand anything", the correct approach is more like, "Yesterday you talked about adiabatic expansions of an ideal gas, how does that apply to the atmosphere" or "I had some trouble with this point (name inserted here) in the lecture, went home and studied the material, but I still don't get it, could you point me in the right direction".
7. You want to visit your professor no more than a 3 or 4 times a month. Some professors are very picky about their office hours, and don't want to see you outside of them, others are more welcoming, but may ask you to come back. IEHO you want to avoid the first kind, but YMMV.
8. Check how many majors there are in a department compared to the size of the department faculty. You will get a lot more care and feeding if the ratio is smaller, compared to larger. OTOH you want to have an idea of how intellectually active your professors are. Look them up on Google Scholar.
9. Towards the end of the year (not semester), if you are doing well in your major, you want to talk with your professor about doing undergraduate research. You should have a clear idea of what area of the major you are most interested in and talented in. The professor may pick you off for his or her group, or may steer you with a recommendation to a colleague. If you are not doing well in the first course for your major, you may want to reconsider your major.
10. Start thinking about what you are going to do in the summer in November. Applications for summer programs open in November and close in January/February. The deciding factor for an internship is going to be recommendations "Bunny Foo Foo was in my class and got an A, one of five in a class of 20" is the kiss of death. See 6-8. Undergraduate research, internships, the recommendations you get from them and the work that you have done are what gets you jobs, into professional school and more. See Bunny Foo Foo letter above.
11. Books are going to cost you $1K per year. In some courses the books cost more than $200/yr, in others pretty close to it. Reselling books sucks, you get less then you do at a car dealer, and besides which books are useful to keep. Many course/colleges have on line syllabii which list the books. Bookstores increasingly have on line sites that allow you to pre-order books. If nothing else this may help you avoid the line from hell that forms outside the bookstore before classes start.
The bad news is that publishers have a whole bunch of tactics to stop you from buying used books, including bundling on line homework systems (these systems are actually a very good thing) at low price with new books and selling the license at high price alone. Several states have now passed laws forbidding such bundling but they are not yet in force. Next year.
Another tactic is for publishers to change editions every three or four years. Most of the time all that they change is the problems. Ask the professors if it makes a difference if you buy the old version, a lot of time it does not.
Non-obvious places to buy textbooks are outside the US, the same books (watch the editions tho) are much less expensive elsewhere and available in paperback, this includes such third world countries as England, France and Germany. Shipping may be an issue, but if someone you know is going over there and willing to lug the book back (textbooks are increasingly the Osborne's of portable books). . .
Primarily for science majors:
12. NEVER take non-calculus physics. Physics without calculus makes no sense.
13. If your math SATs were under 550, take a college math course (probably algebra) before you try chemistry. Eli has been tracking this for years, as have a number of friends at the Carrot Bar Around the Corner from the Chemistry Building. Our experience is that SAT's, math pretests and such show that there is a minimum grade you need to have any chance of passing chemistry, but if students are above that minimum the course grades do not correlate especially well with the math grades. Taking college algebra and getting a good grade (if you don't you probably should not take chemistry) improves the odds no end.