I just studied for my GRE so I have some good experience with a lot of the services.
1. Buy the official GRE guides. Verbal, Quant, and the Overall Book. Do the 2 free practice exams and I would even consider buying the two additional practice exams because they offer explanations and a diagnostic. You can find explanations online for the two free exams. These sections should be done under test conditions.
2. I used Magoosh extensively. I would use their study plans as a basic rough guide. Their verbal section is excellent and very comparable to the exam. The best part of their program is free though. That is their vocab flashcard app. If you do anything study these flashcards so you know the "GRE Definition" of each word.
The negative part of their program is that they don't zero into your problem areas. I only recognized this late and that was my mistake. Also, if you follow their guide then you learn about certain important subject areas, like reading comprehension paragraphs, only at the very end of the study plan.
I didn't like that they would have you answer all different types of questions in practice instead of focusing on one area.
3. I used Manhattan GRE's 5lb book also. It has a huge amount of questions. That combined with Magoosh is just an enormous amount of questions for you to go through. However, I didn't like Manhattan's vocab questions. I didn't use them. Their fill in the blank questions and matching questions for vocab were incredibly dependent on needing to know their list of vocab words, which doesn't match words ETS uses in their own books and tests. Stick with Magoosh for vocab questions.
4. I watched a lot of youtube videos on harder questions like strategies for hard RC paragraphs and DRT questions. Find your weaknesses and find people on youtube who teach these subjects.
5. Magoosh recommends you read from different sources that are more technical and about subjects that don't interest you in order to get used to reading and retaining information. I found their recommendation of the website Arts & Letters Daily for a constant source of different articles. Make sure to write summaries of these articles. Very simple translations of the sentences and main points. This will help you get used to interpreting information the way you need to on the GRE.
I ended up getting a 326 on the GRE. 167 Verbal and 159 Quant. The Verbal was about where I was testing and the Quant was about 5 points lower than I was testing. I wish I had focused more on my problem areas for Quant rather than follow Magoosh's plan of general learning most of the time. Oh, I should add I'm a non-traditional student. It's the first time I've studied algebra since the Clinton Administration:)