Well it depends on what your level is like now, but for me Magoosh (the quant lessons and practice questions), Manhattan flashcards and of course the Powerprep practice tests have been useful. I spent about a month on Magoosh quant lessons but I've been using the flashcards for quite a while because I'm not a native speaker (and neither are you I guess), so rather than trying to learn all those words in a short time I just brought those with me everywhere for some quick practice in between.
I should add that I have a full-time job though, so maybe you can have a decent result within a month, but the sooner you start the better.