Here's something I posted a few days ago to help someone else. It's how I got a 5 on the APES exam by self studying last year, without the class.
Last year I self-studied for the APES exam, and I got a 5. I spent 2 hours a day for 3 weeks studying it. However, I did have extensive background knowledge in science from my studying I did for Science Bowl. I already knew all the chemistry, biology, and earth science that was on the test.
What I did to study was first get the Barron's APES Study Guide. It has MC practice questions and a practice essay at the end of each chapter, and 2 full practice tests at the end of the book. I did all of the practice questions, and checked my scores. I got 73% and 78% on the MC sections...which wasn't too good. But I did very well on the practice essays.
I decided to concentrate on the essay section, since getting 100% on the essays means a 60-70% MC score will be good enough to get a 5. I downloaded and printed out ALL of the past essays that college board has released, they have them for about 10 years. You can find these here: AP: Environmental Science - Sample Questions & Scoring Guidelines
Each day for 2 weeks, I would go to the school library right after school and do the essay portion of one year's test. Then I would look at how the essays were graded, and see how well I did. If I missed points somewhere, I'd rewrite the essay to get full credit on it. Eventually, I had figured out all the patterns that come up and I had a go-to list of examples to call upon whenever needed. E.g., If asked for a toxin write about mercury, if asked for an invasive species write about striped zebra mussels, if asked about ways to make a house "greener" write about passive&active solar design and double-paned windows. I found patterns in what 4 essay questions they asked each year: There's always 1 math based question that's just dimensional analysis, there's always one question based off of reading a document like part of a newspaper, there are always 2 questions that go in-depth for a specific environmental concept, like do you know EVERYTHING about forest fires? Do you know EVERYTHING about nutrient cycles?
With practice, you will get better and better at the essays until you get full credit for each one. You will build up a list of go-to examples that you can always write about in a pinch. The way it's graded, for each question there's a list of all the different examples that could have been used to earn credit. When you look at EVERY released answer key, you see that something like "mercury" might show up EVERY time a toxin is asked for. So that's a good one to use for that. Soon you'll be an essay-writing machine if you do this every day for 2 hours or more.
I don't really know what to say for MC, since there really isn't very much released in the way of practice questions. All I can say is, know your science. The MC questions seemed to have a lot more chem, bio, and earth science than the essays, which were almost strictly just environmental. It helps to have a good background in those sciences like I did, but it's not necessary, as long as you have studied it enough to get about 60-70%, provided you get 100% on the essay section.