Hi gotoeurope.
Four words: Topic by topic practice.
Here's what I mean in more detail.
Go over your practice tests and the practice questions that you have answered to find less strong areas, and strengthen those areas one by one to drive your quant score higher.
For example, let’s say you were to find that Number Properties is a less strong area. First, you should develop as much conceptual knowledge about Number Properties as possible. In other words, your goal will be to completely understand properties of factorials, perfect squares, quadratic patterns, LCM, GCF, units digit patterns, divisibility, and remainders, to name a few concepts. After carefully reviewing the conceptual underpinnings of how to answer Number Properties questions, practice by answering 50 or more questions just from Number Properties. When you do dozens of questions of the same type one after the other, you learn just what it takes to get questions of that type correct consistently.
Since you want to score Q51, your accuracy has to be close to 100 percent. So, if you aren't getting close to 100 percent of questions of a certain type correct, go back and seek to better understand how that type of question works, and then answer more questions of that type. Number Properties is just one example; follow this process for any quant topic in which you are not super strong.
When you are working on learning to answer questions of a particular type, start off taking your time, and then seek to speed up as you get more comfortable answering questions of that type. As you do such practice, do a thorough analysis of each question that you don't get right. If you get a permutations question wrong, ask yourself why. Did you make a careless mistake? Was there a concept you did not understand in the question? By carefully analyzing your mistakes, you will be able to efficiently fix your weaknesses and completely master each topic.
So, work on accuracy and generally finding correct answers, work on specific weaker areas one by one to make them strong areas, and when you take a practice GMAT or the real thing, take all the time per question available to do your absolute best to get right answers consistently. The GMAT is essentially a game of seeing how many right answers you can get in the time allotted. Approach the test with that conception in mind, and focus intently on the question in front of you with one goal in mind: getting a CORRECT answer.
If you want even more information on how to increase your GMAT quant score, you could read the following detailed post.
How To Increase Your GMAT Quant ScoreAlso, feel free to post back with further queries.