I practiced the RC from the MCAT princeton review book and would highly recommend it. It helped me score a 23 in the RC and I'm not a native speaker. I had started practicing from the DAT RC stuff (Kaplan blue book, electronic practice tests I bought online) and was kicking ass because they were so easy and targeted the old type of RC sections, the ones in which the answers are straight forward............lately the RC section has included more and more tone/infrence (sp?) type questions, the MCAT reading section prepares you well for this.
If I were you I would start off with a RC section from the DAT book to get my feet wet and then practice with the MCAT stuff. Do buy and practice some of those electronic DAT tests and do them every day for a few days before the test as they will help you with timing and give you valuable practice in taking the test on the computer (this is key).
Also some people reccomend reading the first paragraph of the reading portion, going to the questions, answering them, skimming the second para, answer questions type of approach. I would not reccomend this as the RC now seems to have a lot of tone/title this essay type of questions. I read(note-did not skim, but read it fast) about half of the essay at once and then answered questions. Key to this section is practice, practice, practice............................oh and luck helps too as some of those RC are impossible