Visit MBA.com and study the basic information available there on the GMAT and the critical reasoning section. View the sample question provided.
Understand that the critical reasoning questions are designed to test you in three main areas-argument construction, argument evaluation and formulating and evaluating a plan of action. You must recognize the basic structure of an argument, identify the various strengths and weakness as well as recognize efficiency factors of a given plan of action.
Study the basic concepts of argument analysis such as premise, example, evidence and conclusion. The critical reasoning questions on the GMAT ask you to evaluate the argument, not determine if it's correct. You must know the different facets of an argument's construction.
Take multiple practice tests. Find them for free on websites such as 4tests.com. Check with your university for other practice test opportunities.
Visit your area library and check out a study guide. These guides offer sample questions, summaries and study tips for all sections of the GMAT.