From my experience, the best way to improve your score is through practice. You must know all the rules cold first. The gmat is all about rules and the basics. The gmat tries and tricks you by making the basics look extremely tricky. You only get screwed when your foundation isin't 100% solid. If you really want a 600, do the following:
1) Go through the mgmat books
. Make sure you know every rule cold: example a line is perpendicular when the slope is the negative reciprocal. I cant emphasize this enough.
2) Get Jeff Sackmans Total gmat. This is the practice. He uses the same question logic, whatever that means, and has created a ton of questions. Once you do all of these, they will become second nature and you will be exposed to so many different types of scenarios. If you do all of this, I can guarantee your score will go up.
Conclusion: You can ask these questions and read posts all day. However, at the end of the day you have to do the work. I started off with a 530 diagnostic score. I was scoring in the low to mid 700's before my real gmat. This came through practice, practice, and practice. Seeing a ton of problems will get you extremely conditioned.