I benefited a lot from other people's GMAT experience on this forum so I will do my bit here to help future GMAT takers.
I got the ball rolling by taking a couple of diagnostic tests - one from the GMAT OG and another one from the Princeton GMAT review. I hadn't taken any standardized tests since my GRE about 7 years ago and I wanted to know my weak areas. I realized that I was the weakest in Sentence Correction (SC) and Data Sufficiency (DS).
But I immediately made a big mistake after that. Being a non-native English speaker, I assumed that the best way to improve my Sentence Correction would be to beef up on my English Grammar theory. Good idea but did not work too well in practice because I wasted too much time mucking around Grammar books, time I should have spent working on actual questions. Moral of the story - brush up some theory in your weak areas and then get down to doing actual questions - as many as you can - but make sure that you attempt questions from a reputable source with good explanations for the correct answer rather than just an answer key.
These are the books I followed.
Manhattan GMAT
Equations, Inequalities and VICs
Geometry
Reading Comprehension
Sentence Correction
Word Translations
These books are excellent and it makes sense to get all of them (they have 8 books, I got 5 of them) if you can, even if you consider yourself to be strong in an area. They are about 20 bucks each at Barnes and Noble (B&N) and cheaper if you have their membership. I consider RC to be my strongest suit and even then, I benefited from their RC guide.
Kaplan 800 and Kaplan Premier Program
I got these books pretty late in the game and wasn't able to complete them comprehensively, but I'd say they were still helpful, specially Kaplan 800.
Tests
Again, Manhattan GMAT online tests were simply incredible. I completed their free sample test and 4 of the 6 tests that you can access by buying any one of their books. Just keep in mind that you will not make any big improvement in scores if you just take the tests without evaluating them afterwards. It is important to go through each and every question after you complete the test and here Manhattan GMAT's tests are again a winner because of their excellent explanations.
Took 1 test each from Kaplan and McGrawHill GMAT CDs and a free test that is available at McGrawHill's website.
I obviously took both the practice tests with the GMATPrep but wait until at least 10 days before your actual test date to take these tests.
I also did all the questions in the GMAT OG, GMAT Official Verbal Review and GMAT Official Quant Review. I used the stopwatch feature on Manhattan GMAT website to attempt these questions - very helpful.
Test Scores
Manhattan free practice exam: 690
Kaplan: 650
GMATPrep 1: 720
Manhattan Test 1: 700
Manhattan Test 2: 720
Manhattan Test 3: 730
Manhattan Test 4: 740
GMATPrep 2: 750
The Real Thing: 760
Dos
Attempt as many questions as you can from as many reputable sources that you can. By reputable, I mean any source that gives you a good explanation of the correct answer.
Take as many CAT simulation tests that you can.
Treat OG and Verbal and Quant reviews to be the bedrock of your preparation.
Spend some additional time on reviewing Math material like Permutation/Combination and Probability online. Not a single book covers these topics comprehensively but you will find a lot of resources online
Definitely get the sample laminated scratch pad from ManhattanGMAT. You can get that too from B&N at a lower price than from ManhattanGMAT.
Donts
Don't waste your time in chasing dubious online material like the GMAT sets. These sets and many other online questions do not have any explanations for their answers, just a cryptic answer key. Surely, you can post questions from those sets on various forums but there is enough material out there in the form of mainstream books and believe me, they are more than enough to help you get a good score.
Don't waste too much time in "learning" theory. Brush up enough to get yourself started and then learn as you attempt the questions.