If you take a long term approach, reading is the best practice for improving your reading. Like most everything else, the more you read the better you will get at it. Imagine playing tennis against someone that plays once a month to playing against someone that plays several hours every day. Read rigorously every day and you will improve.
If you have several months before you plan to take the test, consider increasing the amount of reading that you do each day. I would suggest national newspapers as the GMAT tends to take it's grammatical cues from these sources. The Washington Post, NY Times and Wall Street Journal are best; and in addition to improving your reading skills, you'll also develop analysis skills with subject matter like finance & science that are topics in GMAT questions.