Plan to work.
Colleges - and faculty - expect you to put in a significant amount of time over the course of the semester. At the undergraduate level, a 3 credit course generally meets for 45 hours during the semester. In most cases you are expected to put in 1 to 3 hours for every hour of class time. So, for a class that meets 2.5 hours a week, that means you should plan to spend 2.5 to 7.5 hours outside of class preparing for class and studying the material each week. You likely won't spend the maximum time on every class every week - it's a big time commitment! But recognize that some classes will require relatively little prep and others may require additional hours of work. In addition, the amount of time you spend on each class will vary over the semester.
Get a head start.
This one is simple: Begin early. Read ahead. Try to stay one reading assignment ahead of class. First, this permits you to see the big picture. Readings tend to build on each other and sometimes you may not realize that you don't understand a particular concept until you encounter a more advanced concept. Second, reading ahead gives you wiggle room. Life sometimes gets in the way and we fall behind in reading. Reading ahead permits you to miss a day and still be prepared for class. Likewise, start papers early. Papers nearly always take longer to write than we anticipate, whether it's because we can't find sources, have a hard time understanding them, or suffer from writer's block. Start early so that you won't feel pressed for time.
Get your head in the right place. The first day and week of classes can be overwhelming with new lists of reading assignments, papers, exams, and presentations. Take the time to map out your semester. Write down all classes, due dates, exam dates. Think about how you will organize your time to prepare and get it all done. Plan time off and time for fun. Think about how you will maintain motivation over the semester - how will you reward your successes? By mentally preparing for the semester ahead you put yourself in the position to excel.