I worked with Kaplan verbal and a little with the GMAT big book (the GMAT review).
1. Start with the Big Book and end with the Big Book. This is and should be your "Gideon's bible" all along the journey. Sleep with it, over it and around it. I got waylaid by others on the way and wasted some time before coming back
2. If you are good at quants already, do the last 50 questions in math and the DS sections. I found that part marginally challenging. The DS can be difficult because it requires a different approach than solving problems. GMAT traps you with common assumptions we make when solving problems with known numbers. You will beat these traps with practice.
2. In verbal SC, make sure you understand the reasoning behind each and every question and answer in the Big book. Use Kaplan verbal for help. There are about 5 major rules and the questions in the book cover the questions you will encounter on the GMAT. I also recommend the book available on this website. Just search for majortests.
It costs about 200 INR and is very useful, especially if you are a language guru already and need fine tuning. I bought this book. (I am not affiliated to this website in any way.) It is a very good compilation of fundas but poor reasoning.
3. In verbal, CR is nasty. Somehow, I always found this to be the PITA. This requires a style of interpreting questions and comes only through practice. The Big book ought to be your final stop. Kaplan CR does not reflect the GMAT CR much. Spend more time on CR than on SC. The easiest CR can jack you up and mess your score while the easiest SC will often go your way.
I had scored 720 and 760 on the GMATPrep and got 730 on the GMAT yesterday. I got 640 on all of the 5 kaplan tests. I spent about 45 hours including tests.
Let me know if you need further help. I am just fresh out of the exam hall. I touched a little of Princeton, Manhattan and Barrons on the way, but I simply got messed up. I ought to have spent that time with the Big Book. Use one of these to help you, but just work through the Big book.
biRam