Amanda Morris, College Professor, Writer, Advisor, Writing Coach
Great advice so far, so I will add this. Using the resources available to you at your university will help you to be successful. For instance, the university writing center will help with any and all writing assignments for courses. There are often Student Achievement or subject-specific tutoring centers that will help with everything from study and time management skills to help with biology, math, chemistry, languages, and other subject areas. Look also for a career center - many universities offer career-related preparation and services such as resume reviews, help with writing job application letters, and searchable internship databases.
Finally, creating a strong social network of peers and building a rapport with many professors will provide you constant support and encouragement. And those professors that you build relationships with (take your favorite profs for more than one course, stop by a few times a semester to say hi and catch up) will be willing to write you highly specific and top quality references for scholarships, jobs, internships, and/or grad school.
As my colleagues here have noted, success in college requires much more than a good GPA. By developing strong relationships and using your university's resources, you will not only succeed in college, but will also be well-prepared for post-undergraduate life! :)