To prepare for the AWA, I looked through all the essay questions in the back of the OG and brainstormed in my head about what I'd put down. I checked off the ones that I thought would give me major problems (the really bad ones to which I'd have no intelligent response). Then I just looked up some info and brainstormed some more to get an idea of what I'd write.
I also used books like Princeton Review
to generate a template for each question type.
For the analysis of an argument, I approached the essays as I would the Critical Resoning portion of the GMAT. I basically deconstructed the argument based on how you'd deconstruct an CR problem (attacking assumptions, questionable statistics, etc...). Analysis of an Issue was more on the fly... It seemed to work well...