Practice using GRE vocab words in context. Merely memorizing terms won't suffice. Merriam-Webster has great examples https://www.merriam-webster.com/dictionary/incredulous Write your own sentences using the words as well :D
https://www.amazon.com/Merriam-Websters-Vocabulary-Builder-Merriam-Webster-ebook/dp/B003IS768K/ref=mt_kindle?_encoding=UTF8&me=&qid=
this is also a great resource.