Hello Viki,
Sorry for the late reply!
I will assume the worst possible scenario and give you ideas to get to the highest possible order of vocabulary!
Okay keeping jargons aside!
1. I would recommend the book of Norman Lewis ('Word Power Made Easy') to you! Its cheap and very very effective (from my personal experience). The book will change your perception towards the English language and will help you absorb a lot more when you read.
2. Start reading regularly. Read newspapers (for example- Hindu, TOI, etc), read scientific journals regularly (even twice a week will do).
3. Watch British drama series or good US ones eg: Da Vinci's Demons, Game of Thrones, House of Cards etc. They use a lot of good and esoteric vocabularies and its both fun and learn at the same time.
4. Application is must. Just learning stuff is never enough
To test how good you have progressed in building vocabulary its best always to look for practice softwares like
http://gre.graduateshotline.com/.
You can find better ones too! At the end of the day learning the meaning of a word is not enough as it was in the Old GRE pattern. The bigger context and applicability of the word is very very important to get those critical 3 blank Text Completion Questions right.
I hope its helpful.
Best of luck..