AP classes are not designed to be difficult courses with super-advanced material that you would only learn in college. The reason that they are generally labeled as "hard" is due to the fact that you're learning much more information in a shorter amount of time relative to your other non-honors classes. Most of the knowledge that you need to obtain a 4 or a 5 on the AP exams will come from your teacher and your own effort or your motivation to succeed. Of course, there are certain habits that you can form to boost not only your grades in the class(es) you are taking, but also the AP exam(s). Here are some good guidelines:
1) Do not avoid the summer homework, and do it now if you have yet to start it. Odds are that if you have not done the homework yet, it will settle until the last week or so of your summer. The absolute worst way to walk into your classes on the first week of school is to be burdened with your stress, so try to do it early (and with some effort). Many people (including my friends from high school) tend to believe that your first homework assignment is useless to try on. If you're in an AP English/social studies course, odds are that you had to read a book and then write an essay on it. From experience, those are the ones that take the longest time. If you have a stack of homework to do, make sure you prioritize which ones to do first. Even if the material that is on the homework does not seem like something that will be tested on the first exam or essay, you do not want to miss out on the easy points to keep your grades up. Why start off the year with a 0/10 when you could have a 10/10?
2) AP classes, historically, have a great deal more homework to be done that non-honors classes. Make sure you do every homework assignment, no matter how boring or easy it may be. Not only do you get credit for doing it, if there happens to be a pop-quiz the next day, you'll know all the information you need. Since most AP courses require you to read a certain number of pages in the textbook as a part of the homework, it is always important to remind yourself that you are reading to gain information rather than just to finish the chapter. If you like to annotate or take notes, a good tip is to read the book first, then go back again and scribble in your book or notebook.
3) Be organized! Remember that your teacher is the one person that knows best what will be on the AP exam. Therefore, if you take notes on what they are saying or writing on the board, you have a better chance of scoring higher than someone who does not. Simply relying on the teacher, however, will do you no better than relying on the textbook only. Utilize all your resources and your efforts will pay off. Of course, it is no good if you forget all the early material for the AP exam. Keep a little box in your closet to accumulate notes, notebooks, and homework from your AP classes. At the end of the year you can take everything out and organize your papers between different classes (if you hadn't done so already). If your notes were succinct enough, then you would pretty much be revisiting your teacher's knowledge.
4) Your goal is to score high on the AP exam. Students forget that the reason they go into an AP class is to get college credit (although, I suppose some do it for the 5.0). If there is a slump in your grade because of a past mistake that you made, do not let it bother you. So long as you have learned from your past errors, then you will be making progress for a high grade on the AP exam. You will be thoroughly tested on almost everything you have learned in your class, so if you know that there was a certain chapter that you didn't quite grasp before, solidify your foundations via speaking with your teacher, working on some old homework problems, or simply going over the exam that you couldn't score well on. There is no reason to get caught up over bombing an exam - everyone has done it at least once.
5) Be healthy. I made an enormous mistake of not being physically active during high school. During the summer before college, I started hitting the gym and noticed both physical and mental differences. The stress that you experience during the day vanishes after working out and you subsequently feel a whole lot better when you go home and rest up. Initially, working out wasn't very appealing to me; although, as time went on, it seems like I was conditioned to enjoy going to the gym, simply because it made me feel better, both physically and mentally. There are too many benefits to list on a blog post, but a simple Google will give you excellent reasons on why being physically active is extremely useful for your present and future.
Good luck!