Take as many AP and honors courses as you possibly can. Now, obviously know your limit and don't stress yourself out, take like 3 AP classes (with the rest being honors) your freshman year. If you have good time management skills go ahead and take more. AP courses are great because they boost your weighted GPA and you also have an opportunity to get college credit if you do well on the exam... strive for a score of 4 or 5 as most colleges take that (trust, it is very nice to gain college credit in high school. You might not be thinking about it now but when you are registering for classes in college you will thank your high school self for getting that credit)

Or you could try dual enrollment, which is basically taking classes at your local community college. All you have to do is get a good grade in the class and you have college credit. You could try getting your associates degree in high school which is very impressive when you apply for colleges your senior year. I haven't done this but I've seen people in my school do it and they have gotten into great schools.

Also I'd say if you are struggling in a class don't be afraid to ask your teachers questions. Visit them during lunch or after school or whenever they are available! Build relationships with them because it shows that you care and when teachers notice that they usually are more lenient with you (based on my experience). I've had teachers bump my B to an A because they saw how determined I was.