My GPA first semester of 9th grade was 3.97, second semester 3.5 something, with no honors classes.
It's really not that hard, you just need to ace the assignments that are worth free points. In math class and physics, you got a perfect score just for turning it in, and then a second grade based on the correctness of the work.
If your teacher grades on participation, just read what the discussion is on and figure out some points in the discussion where you have something to add. I got a 99 percent for the first semester of World History doing stuff like that.
If by starting school you mean college, then here are some simple truths to live by:
GO TO LECTURE: Unless you A) are one of the lucky kinda of people that can just read the book and pick up on the material or B) are unlucky and get a horrible lecturer (It will happen eventually), you will want to go to lecture as often as possible.
GO TO ANY CLASS THAT GRADES ON ATTENDENCE: It's free points and unless you have something that is urgent, it's in our best interest to go.
STUDY, DON'T CRAM: Trying to cram at the last second isn't that great of an idea. It's better to go over stuff after it was just talked about in lecture. It's better to re-inforce what is fresh in your mind than try to learn it almost completely new before a test.
READ THE BOOKS: YOu're gonna have to sepnd hundreds of dollars on them, might as well read em. One technique a friend of mine used that got him 90s constantly was to read the book and take notes from the book, then study the notes.
TRY TO SCHEDULE CLASSES CONVENIENTLY: If you are a morning person, then by all means shcedule classes in the morning. I had an 8:00 AM lecture that I was almost incapible of getting up for.
DON'T OVERDO IT: I knew some girls that were 4.0+ studets in highschool, assumed they were smart enough to take extra classes, and then flipped out when they got less than stellar grades. You don't need to get everything done at once. Pace yourself.
Usually an "A" in an honors class gets you a 4.5, and an "A" in an AP class gets you a 5. Some schools, especially intensely academic ones, don't weight their GPA. At my school an honors "A" is a 4.1, and an AP "A" is a 4.2.