The writing section of the GRE is the (IMO) easiest section to prepare for and improve on. Every prompt is listed online, so there shouldn't be any surprises when your topic choices pop up. Each prompt falls into categories like science, education, humanity/society, technology, government, etc. I copy/pasted all the topics into a word document and then arranged them in groups by topic theme. Then I went through each section and made sure I had 3 examples/references to support my view on the matter. For example, the prompt:
"Many people know how to attain success, but few know how to make the best use of it."
I decided I would show 3 examples of people who did not make the best out of their success: robert koch, kurt cobain and heath ledger. I would then demonstrate a few people who DID: donald trump, steve jobs...
It may seem like a lot of work, but once you start thinking of specific examples to support your position, each prompt gets easier and easier.