Here are a few tips for increasing your quant score.
It almost does not matter what you work on as long as you are working on something that will increase your score. So just keep finding aspects of GMAT quant at which you could be more effective and work on them one after the other.
That having been said, in working on practice questions, focusing on one topic at a time tends to work best. In doing that you give yourself opportunities to really hone your understanding of and skills in handling questions of each particular type.
Meanwhile, many points can be picked up by just being tricked less. I mean without learning one more math concept probably you could increase your score by seeing more clearly what's going on in, for instance, DS questions that use simple math in a tricky way. There are many questions that just use fractions or exponents to make you think, and people don't get them right even though obviously they totally understand the math.
For example, in a previous post you said that numbers that end in 3, 6 or 9 are divisible by 3. Figuring out that that is wrong does not require understanding complex math. It requires seeing the logic of the numbers.
So seeing logic is much of what you need to work on, and in your mind you need to develop a matrix of understanding more than you need to memorize. It's easy, for instance, to remember and apply a formula if you really understand what underlies that formula. In essence you are best off being able to recreate a formula because you understand so well how the formula works.
In any case, you can get a lot of mileage out of getting good at seeing more clearly, as to a large degree GMAT quant is a test of VISION.
Key to developing understanding, skill and vision can be playing the game a lot, by learning how to do things and applying what you learn repeatedly in a variety of scenarios. Just like anything else that you do, GMAT quant can become more natural the more you play it. Don't play haphazardly though. Be intense and tend to work slowly and carefully with a focus on truly understanding and on getting right answers to practice questions.
To save time, there are, in addition to divisibility rules, things you can get good at.
Get good at working with the dimensions of geometric shapes. You can save time by being good at getting from the area of a circle to its other dimensions and vice versa. You can save time by being good at getting from the area of an equilateral triangle to its height or to the length of its sides.
Learn to recognize these key Pythagorean triples, 3 - 4 - 5 and 5 - 12 - 13. Also be good at recognizing and working with 30 - 60 - 90 triangles.
Get good at figuring out the factors of numbers. A great exercise that you could do is to figure out the prime factors of each number from 2 to 100. Count by primes, 2, 3, 2 x 2, 5, 2 x 3, 7, 2 x 2 x 2, 3 x 3, and so on. Being good at finding all of the prime factors of any number can save you LOTS of time.
Know the squares of all the numbers from 1 - 20 or at least play with each of them once or twice so that if they show up on the test you can pretty quickly recognize them. I say definitely know the squares of all the numbers from 1 - 12, and know that 15 x 15 = 225 and that 25 x 25 = 625.
Be good at counting by 15's and 25's.
Another set of things to be good at recognizing is the special quadratics. If you can readily see those when they show up, you will be much more likely to quickly answer certain questions.
I have seen people who thought that they were "not good at math" develop and drive their quant scores up point by point. They just played the game and learned and got better, and people tend to realize that in a sense we are all math geniuses. We just need to tap into that and develop ourselves. So just remain determined, develop your vision and keep looking for ways to increase your score, and you can be sure that you will.
