Assuming you are applying next Fall:
- Read online articles from news and magazine sources. Bookmark them and read a bunch every day. It doesn't matter what the content is, as long as its in English and not a blog or some media source which doesn't have professional editor. The Economist
, BusinessWeek, Washington Post, The Onion, HuffPost, AskMen, chick stuff, whatever. Read a bunch of articles every day on any topical online sources which are of interest to you.
- Do the same thing with books if you like. Fiction or non-fiction. Haven't read much but want to read something that makes you laugh? Go get any one of P.G. Wodehouse's books - anything in the Uncle Fred series is great. You'll keep entertained. If you run across a word or phrase which doesn't make sense, look it up. Or start reading romance novels if you're a girl; every girl I know seems to be addicted to them.
Probably says more about me than them.
- Write short stories in English or start a blog and make a post every day on it on anything
you like. Weather, varieties of kittens, cartoons, whatever you like.
Do these everyday for 2-3 hours for 6 months and you'll be amazed how dramatically improved your English is, even though at the start on a day-to-day basis you may feel you're not improving or not by enough.
Reading a lot is important for those not comfortable with English because:
1] This will help you more than anything on RC
2] SC relies on having an 'ear' for English, with high level rules used to 'close the gap' to the tight solution. it isn't possible to memorize every possible rule of the English language and apply them in 1:30 to a problem. You can go about memorizing idioms and such (I haven't and am not going to), but unless you have an ear for grammar, you'll struggle on the medium-hard questions. The only way to get an ear is to read lots.
3] CR is about logic, not grammar, but you still need to have a decent grammar to clearly make out the logical connections between statements and their validity.
Read like a typhoon for a few month and then look over these forums for GMAT specific book suggestions. I wouldn't
go straight to the CR and SC books people suggest to master for a 700+ score before you get a fluency for grammar. The best way to do that is by reading a lot, not memorizing a thousand rules.
So an example of your plan would be:
A] Read like crazy any
material in English: 4-6 months. Say Dec - Mar. If you start with GMAT material right now you will cause yourself a lot of frustration and despair, especially if you want a 700+ with below-average (compared to native or native-like English readers) overall English comprehension.
B] Start GMAT prep in April. Take the free MGMAT Test. Depending on your score grab the appropriate materials out of stickied threads.
C] Take the GMAT in June. Start working on Essays etc.
D] In case something goes wrong, you happen to be sick or get the nerves on test day, you can take the GMAT again in July.
Disclaimer: I haven't taken the GMAT yet myself, so take this for whatever its worth. If someone comes around with a 750+ score in their profile, take their advice more seriously than mine.
The only ability the GMAT is an indicator of...is the ability to do well on the GMAT.