Pay attention to your performance in high school. The higher your high school grades and the better-rounded you are by participating in a variety of sports and other extracurricular activities, the better chance you'll have of being accepted to your first-choice college. Take the SAT or ACT if you have not previously done so; many colleges require one of these scores to be submitted along with your application. Find out if any of the schools in which you're interested require you to take one or more of the SAT subject tests.
Educate yourself on the admissions requirements and deadlines for the schools on which you're planning to applying. The College Board says many students begin working on their college applications during the summer prior to their senior year so they'll have plenty of time to perfect their application packages.
Complete a Free Application for Federal Student Aid (FAFSA) around January of your senior year. This will help you determine which schools you and your family will be able to afford with the help of student aid. The California Student Aid Commission also has financial aid programs available for California residents who attend an in-state school such as California State University or the University of California.
Fill out your college applications carefully and honestly to give the admissions staff an accurate idea of who you are and what you will bring to their school. Check with each school to determine if they prefer online or paper applications, and also talk to your guidance counselor to find out what forms your high school will send out for you. A typical application package includes the application itself, an essay, your high school transcripts and SAT or ACT test scores, letters of recommendation and the application fee.
Schedule an interview if any of the schools to which you're applying offer or require them. They often aren't required, but by requesting an interview anyway you will show you are serious about college, which may help you gain admission. This also gives you a chance to make a good impression on a personal level beyond the list of credentials in your application.