Here is some advice based on my college track career. Admittedly it was 25+ years ago, but I think it probably still holds true.
Class, class, class. Make sure you are attending class and keeping up with assignments. Its so easy in college to start to blow off class and assignments. I know right now your saying, yea no problem, but its tough to get to that 7pm class after having practice and weight room until 6pm. This needs to be you number 1 priority. Many schools will have athletic/academic staff and may require you to attend study tables until you can prove you are able to survive and pass classes on your own.
As others have said, come into it in the best shape of your life. For the most part this has now gone from being a game and is now a job. The coaches expect you to come in in shape, as do the older teammates. They are not going to waste time waiting for you to catch up with the rest of the team. You are now an adult and they expect you to be responsible and ready to go.
Nothing is optional. If its an optional practice or an optional meeting you must attend. The only exception to the rule is if it conflicts with a class. If it does, you will need to get with the coaching staff/academic advisors and let them know.
Make sure you find out when practice is and schedule your classes around practice. Its seems like a simple thing, but the coaches expect you at practice. As you progress through the years you may find that an upper level class conflicts. The coaches will work with you on that, but at the lower level there is usually enough classes that you can schedule around practice. Yes that means you may be in an 8am class or a 6p-10p class, but you need to do what needs to be done to be a student athlete.
Realize that everyone on the team is competition. The upper class-man will view you as that. They will initially see you as attempting to take their positions. You will need to be ready for that. At the same time they are your teammates and will become some of your closest friends. Its a touch balance but you will figure it out.
Finally have fun. The 4/5 years will go by real quick. Its over before you know it.