The best way to develop vocabulary and reading-comprehension skills is to READ, READ, READ!  The GRE is intended to identify students who are very well-read in academic-style English.  Your reading repertoire should consist of a variety of informative non-fiction and expert opinion.  I am recommending a few websites rich in valuable articles for your long-term development.  I advise that you read this kind of material daily.  Look up ALL words you don’t know so that you fully understand the passage.  Select 1 – 3 of your favorite words per day for further development in your vocabulary journal.    It might feel funny to you to stray outside of GRE books, but believe me — this is not wasted time!
  • — Slate describes itself as a “general-interest publication offering analysis and commentary about politics, news, business, technology, and culture.”  A sample article that will be of interest to you has to do with the challenges of graduate school and dissertations.
  • — Articles about scientific developments written by scientific leaders for the general public.  This sample article is about global warming.
  • — This is the online magazine from the National Endowment for the Humanities.  A sample article is about the relationship between 19th century feminists Anthony and Stanton.
  • — Reuters provides news content that is used by papers and websites throughout the world, and is considered one of the most objective news sources.  Sample article about civil unrest in Missouri.
  • The Evolution Of Human …  — OK, this one is a shameless plug.  This is a world history that I am writing.  It is a “logarithmic” world history, meaning that each chapter is devoted to a power of ten years.  This approach allows me to cover all scales of time from ten to ten-billion years ago, so you will find subject matter “from the big bang to big data”.  Most of the technical words have links to my glossary.  Remember that you don’t need to learn technical terms for the GRE.  I finished the first draft of the book in 2018 and am working on the 2nd draft in 2019.  In 2020, I will be seeking feedback from lay-readers.  Let me know if you are interested in participating!