If you can handle the work in honors, Advanced Placement, or other accelerated courses, you should probably be taking at least a few of them. If it is obvious from your transcript that you are taking a lighter load than you can handle, admissions officers at selective colleges are going to wonder about your motivation. Make sure you take some hard classes at the end of your junior year so you don't look like a total slacker.
Virtually all colleges require your high school to update your transcript with a mid-year grade report in the middle of your senior year. Colleges really do care about your first-semester senior grades, so don't mess up! Keep your grades decent or you may really mess up your chances with your top schools.
Many colleges say that class rank is more revealing than simple grade point average. (Most are interested in both.) This is not rocket science: Students who end up near the bottom of their high school classes tend to end up near the bottom of their college classes as well. So, start getting higher grades if you want to move up in the world.
A last bit of advice: Never take a course pass/fail. Admissions officers don't know what to make of a "pass" on your transcript. They may count it as a C or even a D in calculating your grade point average. They will certainly decide that you were coasting when you took that course. At the very least, you should never take a solid academic course pass/fail. (You may have no choice about taking some courses, like driver education and typing, pass/fail; that's not what we're talking about.)
