Aside from the obvious (practice Kaplan
, OG, Princeton, etc.), I have two suggestions:
1. Do a bit of reading each day that is unrelated to the GMAT, even if only for 10-15 minutes. Read the types of stuff you have never read before. Like for economics, read the "Wealth of Nations" or some other stuffy classic. Read something science-related, perhaps from a technical magazine like "Scientific America," where the articles are written in lay terms but can be somewhat engaging and complicated. Also, "Atlantic Monthly" has long, interesting articles. Practice reading, but proactively, not casually. When you read, try to stop every few paragraphs and summarize the topic/concept/argument.
2. In the "Insider's Guide to the GMAT CAT" by Karl Weber, he suggests a strategy which is very helpful: Read the passage three times, and then try to answer the questions. First, read it quickly-- skim, rather. Try to get the main point. Then, read it one time slowly and carefully. Then, skim it a third and final time. When you skim it, try to summarize the topic/main point and also look carefully at the structure. Again: Skim it, read it carefully, then skim it again. That way, when you answer the questions, you are familiar with the passage and know where to look for the answer.
Here is one of my tricks: The answer must be 100%. In other words, if there is any ambiguity in the answer, it is wrong. There are usually three answers which are blatently wrong, one which is ambigious or partially correct, and one which is actually correct. You can usually narrow it down to these two. Make sure the one you choose has no ambiguity.