The final month of studying is one of the most crucial times in the study period, its where you make those final adjustments and fill in your gaps in knowledge. I think there are several key things to be doing in your final month GMAT prep.
1) Find your weaknesses and address them
It is important to fill in those gaps, so they don’t hold you back on test day. If you are bad at coordinate geometry, don’t just hope it won’t come up on the test, because in all likelihood, it will. And getting a very easy question wrong can really hurt your score. In order to pinpoint your weaknesses, you need to take an in depth look at your last few CATs. Note which type and topic (ie SC:modifiers or DS:exponents) you are getting wrong the most and why. It is also important to note if you are getting any easy problems wrong on a specific topic. Then, review those topics through your course or books.
2) Build your mental endurance
The GMAT is mentally exhausting and it is important to train yourself to prepare for this. In order to do this, you should be taking full length practice CATs that simulate the test experience as accurately as possible. That means, only take the allotted 8 minute breaks and do the IR and AWA sections to the best of your ability. I recommend taking at least 10 of these tests in the final months. This will make sure that you are able to fully concentrate for the full 4 hours and help battle test day nerves.
3) Practice with the most difficult questions (for people with goal scores of 700+)
A big part of scoring well on the GMAT is being able to answer the difficult questions. There is no point in starting your study with these, however, because you won’t get to the most difficult questions on the test if you don’t master the easy and medium ones. The final month is the time to work on strategies and practicing for these types of questions. I recommend looking into the MGMAT Advanced Quant and Kaplan 800 books. LSAT questions are also a good resource for difficult CR and RC questions.