Reading comprehension passages are up to 350 words long and can be about anything, but no specific knowledge is required to correctly answer the questions. Before reading the passage, read the question so that you know what to look for. That said, don't select an answer before reading the entire passage. Forming an outline while reading the passage can help you locate details later and provide a summary of the passage to better answer the question. Additionally, eliminate any questions that contradict the author's position on the passage's thesis.
Critical reasoning questions measure your ability to understand and rationalize an argument as well as form one of your own. Always read the question before the passage so that you can have a better idea of what to look for. Identify the argument's "premise" and "conclusion" to help you make sense of non-linear passages. These are often indicated by such terms as "because" and "as a result," respectively. Be aware of red herring statements that add nothing to the argument.
Sentence correction questions ask you to choose the best of five choices that express an idea. Choice A always repeats the underlined part of the sentence. Keep in mind that in one out of five problems, the original sentence---choice A---is the correct one. Don't waste time looking at punctuation, as it is not tested on the GMAT. Answers that distort the meaning of the sentence are usually wrong and can be eliminated. The best choice might not be award-winning writing, but the choice that is the least awkward and is grammatically correct is the best answer.