Reddit reviews Cracking the GRE Premium Edition with 6 Practice Tests, 2018: The All-in-One Solution for Your Highest Possible Score (Graduate School Test Preparation)

The above posters provided some excellent advice. Particularly, to use scratch paper as much as possible. I've started viewing it as insurance against mistakes, and as a way to quickly correct them should they be discovered. Having a trail increases the chance of me recovering from an error, be it careless or logical. It also reduces mental gaps and leaps which in my experience are the most vulnerable to errors. I've focused on this advice the most. So not only am I using scratch paper more for almost all computations, I'm attempting to keep it somewhat more organized as a tactical consideration. Imagining if someone is going to look at your scratch paper afterwards helps a bit.

In addition, I've been studying with two resources: Magoosh and Princeton Review. PR goes through several strategies for quantitative questions to rule out answer choices and to solve problems without a rigorous algebraic approach. Magoosh covers these too in maybe 3 or 4 videos. At first, I scoffed at these strategies because I thought they would not foster an understanding of the topics at hand. As an example one such strategy is "plugging in". Now, I think it makes sense to use these strategies aggressively in problems where appropriate for two reasons. One, solving problems in the most mathematically complete way exposes oneself to more errors and traps. I mean, no one disputes that it's harder to make a proof for a mathematical problem than to guesstimate a single solution. Second, these strategies generally lead to an answer in less time. The goal of the Quantitative portion isn't to prove that you are good at or the best at mathematics. It's not a test for mathematicians. There are tests designed to be taken by mathematicians (by profession) and the GRE is not one of them. The goal is to finish the test and get the most questions correct. I'm not great at math at all, but I somewhat arrogantly avoided approximation strategies because I thought that they didn't do the questions justice and prevented me from learning more. Well- the test questions and the test writers don't care if you can produce robust algebraic proofs and find all the mathematical gems underlying all problems. The test writers (ETS) probably just care that you reasonably attempted to answer every question.

To be clear though, my #1 focus (besides doing 100s of practice problems obviously) has been on solving problems coherently with scratch paper and avoiding mental gaps. I'd say I'm utilizing approximation strategies 25%-33% of the time but am trying to increase this gradually.

Sorry for the late answer and the rant. I've been studying in between since you asked and now and I've considered the question more since then.