I know there's a lot of information already posted on this forum for situations similar to yours, but I would suggest that the first step for any studying would be to take a practice test.
You mentioned that you scored well on other standardized tests, and the good news is that Critical Reasoning on the GMAT uses similar skills to some questions on the LSAT, and both have a Reading Comprehension section, so I would assume you would do quite well on your practice test, particularly in verbal.
So, first off, take a practice test, analyze what types of questions you did well on and which need work, and then think about what books to buy or whether you want to take a prep class or a buy a self study package and go from there.
You can take one free practice test on our site here: http://www.manhattangmat.com/free-gmat.cfm
. When you sign up you also get access to new free guide, called the GMAT Uncovered, which has a lot of information on the GMAT, some strategy tips, and a few chapters on business school applications. That information will definitely help you as you begin studying for the GMAT, so be sure to check it out.
Best of luck as you begin to study, and feel free to contact me if you have more questions.
Student Services AssociateManhattan GMAT
Caitlin Clay | Manhattan GMAT Student Services Associate | New York
Manhattan GMAT Discount | Manhattan GMAT Reviews