Stay focused and committed!!! You can improve and dominate the test! It just takes a lot of work and patience! Improvement will take time to see, but if you follow some of these recommendations, you will see improvement.
1. Read. Read. Read. The first thing that you need to do is improve your overall reading ability. This will have positive effects across all parts of the test. So make a point of reading high quality materials on a regular basis, i.e. everyday. I recommend reading The New York Times, The Wall Street Journal, The Economist, The Atlantic Monthly, MIT Technology Review. These news sources are not only what business leaders read, but they are written at a level that is comparable to the reading on the GMAT.
2. How You Read Matters. I address this issue in a post that I recommend reading. This will tell you how to read so that you maximize the benefits of reading everyday: http://www.urch.com/forums/gmat-read...g-ability.html
3. At Magoosh, we see a lot of students with varying levels of commitment. One thing that we notice that is telling and maybe a little obvious is that the students who answer the more questions do better than students who answer less. But even more than this, students who answer all of our 1000 questions twice will score higher than a student who only answers all the questions once. So there is a benefit to answering a lot of questions and returning to questions that you have already answered. I can see that you have a lot of resources at your disposal. You should plan to go through all of those books more than once. I can say that the Manhattan books will be your best resource since they tend to have the highest quality questions out of all the test prep books. But that does not count the Official GMAT book. If you can't work through all the books twice, you should definitely work through this book twice. Since it is made by the test makers, it will provide you with the best possible preparation. And this means you shouldn't write in the books since you will have to use the questions again.
4. Take Notes. Don't miss the opportunity to keep track of your progress. You should be writing down everything you learn in these books. When you read an explanation take notes on what you learn. FInd a word you don't know—look it up and write it down. Find an idiom you never knew—write down. The more you can track your progress, keep tabs on your weaknesses, the more likely you are to improve.
5. Come up with a study plan.The last thing you want is to haphazardly approach your studies. Map out how much time you have and how much you want to accomplish in that time. Come up with a daily routine that you can adhere to and follow. Schedule multiple shorter study sessions instead of long power sessions. Know what you are going to do next week and next month to prepare for the test. You can also find study schedules in the forums and we even have some at Magoosh too. These would be a good guide which you can adapt to your materials and needs.
I hope that these tips help! Stay diligent and focused and you will find success!