Reading Comprehension in the GMAT/GRE
Getting good at reading comprehension is a life long process. However, since you don't have that long here are some tips.
1) Practice doesn't make perfect. Perfect practice makes perfect. So you have to practice correctly.
2) When practicing reading comprehension really focus on reading faster than you would for pleasure. Reading for the GRE/GMAT isn't like you're everyday reading. Often when we read we are a bit lazy, which is normal when you're reading for fun. However, on the GRE/GMAT you're reading with a purpose so you have to practice reading in the same way you're going to read when you take the test.
3) The average reading comprehension article is 300-500 words. Therefore, you need to practice reading short articles. One of my favorite sites is the the New York Times at www.nytimes.com . An added benefit of this site is that you can double click any word in any article and you'll get the definition. Vocab and the reading comprehension in one! The next best site is probably the Economist.com because the articles tend to be a little shorter than the ones on the NY times.
4) It is also good to just use reading comprehension articles from practice tests. These are the proper length and already have questions that come with them.
5) A good source for practice tests is the GRE official guide, which will give you seven official tests to work from.
6) The Official guide for the GMAT is also a good guide for the GMAT.
7) Make sure that the articles you read vary in topic. Your going to get one article from history, art, science, and economics most probably so practice on several different article types
8) For the GMAT- get good at sentence correction. You should be shooting at doing SC questions in about 1 minute. This allows you to spend more time on the RC passages.
9) For the GRE- get good at analogies by doing lots of them. The better you get at these the more time you'll have to do the RC passages.