I highly recommend the
MGMAT books. As far as how to study them, there was one method that I found helpful. For the math, go through each section in the beginning and do the problems at the back of the book. read any answer explanations for all problems and mark the ones that you got wrong. After you finish the basic topics, go back and read the sections again and reanswer the ones that you got incorrect. You will gain a lot more the second time you go through, after actually applying the concepts. Then do the advance sections. Also, if you are weak in quant, I highly recommend using the foundations of quant book.
I would take a similar method with the verbal books as well. Except go through them each section at a time. Then do the official gmat problems that match the sections. Then go back and reread.
Also, I would suggest doing a CR, SC and math section each day, opposed to focusing and doing only math for a few days, then only CR, etc. One of the biggest things is getting practice with each one every day. I tried cramming them in that fashion and wasted time. For example, I mastered CR and stop reviewing it for a month. When I came back, I essentially forgot / lost each of the tips offered in the book amd had to reread. Doing a few questions of each section a day helps you to build the method and strategy for answering each kind of question, even you only do one problem of that type a day, its a lot better than taking a break.
Also, depending on what score you are shooting for and your weakness, there are other sources that may be better. for math, I found the GMAT hacks tests and supplemented with Veritas prep blog to be more helpful than the GMAT books, especially if you are weaker in quant. But if you do not have a lot of time, using the
MGMAT books is a lot quicker.
Best of luck with your test prep. If this was helpful in anyway, I would most certainly appreciate a kudos.