AP English Language and Compostion
I self-studied for AP English Language and Composition. Honestly, it was very similar to the SAT Critical reading section with the addition of several new literary terms. You need to practice multiple choice questions and make sure that you master all of the different literary terms. I would suggest using the Princeton Review AP English Language and Composition book for practice questions and preparation; however, I would caution against using it for actual learning. The book has pretty realistic questions, but it doesn't really delve into a lot of information.
If you are self-studying, I would suggest (and always suggest) getting an REA Crash Course to English Language and Composition book. They are absolute lifesavers and help you review everything that you need to know.
As far as preparation goes, you should have gotten a lot of experience over the course of your high school career. Frankly, your high school curriculum should have almost fully prepared you for this test. You will need to write three essays; two of which you can do without a terribly large amount of AP Lang knowledge. The first is known as a synthesis essay. This is very similar to the research papers you do in school except for the fact you have to write it in 40 minutes and you have to use the sources given. Overall, if you have written research papers in that past you should be well prepared. The third essay is an opinion essay. You have to take a side on an issue and then write about it (very similar to the SAT Essay section). Finally, the last essay you will need to do some learning for. You have to analyze a work by probing for various rhetorical strategies. The essays are worth 55% (more than half) of your total score, so it would be wise to pick up as many points as possible on the essays.
As always, if you have any questions! Please feel free to ask me!