Keep your partying at a reasonable level. Enjoy yourself, but don't let your social life affect your grades. Put your school work first, and your social life second.
Give your homework your undivided attention. Set up a dedicated study area that's devoid of distractions. Turn off your television, for example, and wait until you've finished your school work to read text messages from your friends.
Visit your professor during her office hours if you have questions. Meeting your teacher outside your regularly scheduled class also lets her know you're paying attention during class and doing the work, which may work to your advantage even after you finish the class. You may need a professor's recommendation when applying for internships or jobs.
Don't procrastinate. Study and do your work as far in advance as possible. Write down all your exam dates and assignment due dates in a planner as soon as you get a course syllabus.