GPA is one of the most important objective measures on your college applications. Colleges use it to not only determine your academic aptitude but to compare you against other students in your high school / county. You can increase your GPA by taking Honors or AP classes (depending on the offering your high school has).
Every year the competition for colleges keeps rising so if you're aiming for a school that has very high average GPA's, it's a good idea to start taking these more advanced classes in 10th grade. They have the added benefit of helping you prepare for college since they are more rigorous.
It's totally possible that your school may not offer very many (or any) AP or advanced classes. If that's the case, you can still take classes at a local community college if you'd like. The admissions officers will always look at your application in the context of the resources available to you.
While many colleges consider your application holistically, and don’t have a minimum GPA requirement, some colleges do have a lower limit on your GPA. For example, University of California colleges require California applicants to have at least a 3.0 GPA and nonresidents to have at least a 3.4 GPA (Source).
Often high school students wonder how they can increase their GPA. A lot of it comes down to studying technique. You'll find that even if you take a very intense workload, by following a few key study habits, you can end up doing much better in your classes.
- If your classes are lecture based, get a head start on the material the night before. Even if you have a basic idea of what the professor will be lecturing about, you will understand and retain a lot more of the material.
- Don't be scrambling to do everything at the last minute. It'll be hard to actually grasp the concepts, and you'll find yourself cramming without much success. A general rule of thumb is if you can't explain a concept to someone, you really haven't understood it, so explain it to a friend!
- Do the homework religiously. It's meant to teach you about the key concepts of the course. If you just copy the answers or don't put much effort into it, you'll be in a really bad position for the exams / final.
- Plan and prioritize. Most classes will give you the schedule ahead of time. Know which weeks are crazy and plan ahead. It's amazing how much you can get done (and how much extra time you'll have!) if you plan out when to do your homework / extracurriculars.
- AP / Honors classes aren't necessarily harder. They just move faster and cover more material, hence students tend to get overwhelmed. If you find that your course load is simply too much, even after following the above tips, you may have taken on too many advanced classes - in this case, it's completely fine to drop a class. Instead of suffering in all your classes, it's much better to do a course load thats challenging, yet still allows you time for your extracurriculars.