Welcome to BTG! I suggest you start with the "Self Study" tab at the top.
Stacey has a nice article of how to develop a GMAT study plan.
A few basic tips:
Start with the Official Guide and MBA.com. Learn the format, content, and do a general overview of the GMAT test itself using the OG 12th edition, and supplement with the Quant and Verbal OG's if needed.
Don't procrastinate! You will need to be disciplined about your studies. Work backwards from your test date. Don't cram on the weekends only! With only one month to study, you'll need to do at least some GMAT every single day.
Get these books: MGMAT SC & Powerscore CR. After the OG, these are two Verbal books that can take your score to the next level.
Track down success stories on the "I Just Beat the GMAT" section. Success leaves footprints, and you'll learn a lot by reading older students' success stories. Find out what strategies are commonly used by 750+ students, what study plans they keep, and how they build their content-knowledge.
Use an Error Log once you get around halfway through. Re-take quizzes and practice tests from the very beginning of your GMAT studies. It will be the best tool to help you assess. You can find many templates online
Take no MORE than 1 GMAT practice test per week. I suggest taking a test every 10 days, which will allow more time to improve between tests.
Good luck, mdr2012!