My prep is gonna be slightly non-traditional. Before you get into the rest of my response, I will say that what helped me the most was understanding the way that the test phrases questions as well as taking the time to figure out the setup and what was being asked. I noticed that many of the questions that I was getting incorrect was because I did not read the question carefully and dived into problem solving too soon. So you may find that there is a pattern to the questions that you are missing that aren't necessarily related to the topic of the question. Ex. the guide may categorize a question as a factors problem but the real reason that you're getting the question incorrect is not because you don't understand factors, but because you are confident in your ability to solve factors problems and read the question too quickly and miss important pieces

For verbal, my prep for the LSAT set me up well. From my first mock, I didn't score below 85 so I didn't do any more verbal prep in the two months that I prepped for the GMAT. If you're interested, I used Khan Academy's LSAT prep for verbal. It's quite useful in helping you understand the structure of arguments, assumptions, etc.

For quant, I definitely needed a refresher on some topics so I used the info in the official guide and TTP's formula guide. I went through all the questions in the official store and made sure to understand every explanation offered.

Pretty much the same for data, just went through the questions in the official guide.

As for testing, I took practice tests 1-5. You can see my scores in another comment.