Dear Mike, please do not rush the job. I am non-native speaker MBA holder aiming to score in the high 600s and hoping to cross 700 even. First time I went through GMAT I was in your shoes. I did little preparation with GMAT prep software and went through basics of Math and relied on my verbal abilities. Despite the fact that I have extensive experience in English speaking environment and sat for multiple computerized tests for professional designations I was able to score only 22 scaled points in verbal part. My scaled points in quants equaled to 25. I did my best at that time, this would be what I thought after the test. One year left and I turned to GMAT again. I need this test score's submission for my PhD application. So, I started over and sat for reading and solving section end problems from MGMAT - all Math guides. Then I quickly scanned MGMAT verbal part. I sat for practice test and WOW - Q28, V20. I tell you what -
YOUR GMAT SCORE IS 30-40% THE RESULT OF YOUR THEORETICAL BACKGROUND. THE OTHER 50-70% COMES AFTER PRACTICE!
Having said that I urge you to read Princeton Review - Cracking Gmat. You must memorize one rule and do not read Facts from OG11 about myths, etc. ... First questions on every GMAT test count more, I would even say MORE. It is the matter of CAT algorithm, the program works this way. Further the truth in GMAT words is if you answer the first 5-6 questions (these place you in score ranges of 600+, 500+, 400+, 400-) and relax for the remaining questions, again you fail the plan. You must read Princeton first to understand how the test program works and then sit for CAT. e.g. - one can be good in general sports but fall a victim of weak physical exercise.
After you go through MGMAT and read Princeton, please do all OG11 or OG12. If you start OG11 and find the questions easy, think further - all OG questions become more difficult as you cross the PS questions after 120 and DS questions after 100. OG questions are placed in order of increasing difficulty.
Realistically you are now where I started one month ago. You need at least two and half months to score 600+. First month goes to working through MGMAT and drilling OG11. The second month will suit your needs for CAT practicing and catching your weakest areas. Most probably you will start your verbal preparation seriously in the second month. You may need CR bible from Power Score then. Learn 100% material contained in Beat the GMAT flashcards for SC. Read OG11 or 12 for RC and find the most suitable strategy for your reading comprehension.
The third month or a half of it goes to sharpening you test taking abilities. You must be prepared for GMAC challenges during G-day.
good luck.
P.S. Believe me after 1 month you will score at least 70% in quant if you leave behind MGMAT and read Cracking GMAT of Princeton Review (CAT techniques).