One thing to know to be successful in college is that higher education can be like a full-time job. Even if you're not taking a full course load, it's likely you'll have to spend many of your free hours studying, reading or attending academic functions. Expect that you won't have a lot of time to work, unless it's at a part-time job. Also, know that college requires you to show up for yourself just like you would at work -- no one will force you to come to class or complete your assignments for you. Success depends on your willingness to show up and do your best.
Another important thing to know about college success is that your relationships are important. Whether it's a professor who is willing to give you an extra credit assignment to boost your grade or a roommate who can help you study for a hard class, people you meet in college are crucial to your success. Get to know as many people as possible, especially your classmates and professors, since you never know who might be able to help you land that internship or tutor you in a difficult subject.
Understand that your college professors, advisers and administrators are human beings who can make mistakes. Be proactive about your own college success instead of assuming that things will be done for you. Don't be afraid to dispute a bad grade, ask for the status of your transcripts or seek out advice if you want to change your major. It's up to you to double-check on important paperwork, your grades or anything else that might affect your academic success.
To be successful in college, it's important to know that parties and social events will be plentiful. Don't forgo studying for a big test to attend a party. While you may not get another chance for a good grade, another party or social function is bound to happen sooner or later. Be realistic about how much socialization you can handle without it affecting your grades. Don't worry about missing out on a social opportunity, since, in the end, a bad grade on one test could affect your grade-point average or cause you to fail the class completely.