I have some things to add:
I studied words from Barron's GRE. But trying to simply mug up the words won't help much, as you would find it difficult to recall the meaning during stressful exam conditions. But you can master the words,
1) Try to learn 10 words a day.
For this, you have to select 10 words - pick them up from opinion page of The Hindu or if you wish, from Barron's GRE.
Then, write it down in a book. Try to formulate sentences on your own. Write a paragraph that uses all the 10 words (helps improve your writing as well).
Next day, read the paragraph and try to recollect the exact meaning of the word. Read for 2-3 days, you will remember them no matter what.
2) Subscribe to the Reader's Digest - it has a word power section, plenty of good articles in excellent English - definitely helps in improving your vocabulary.
We will remember words best if we learn them by continuously coming across them in suitable contexts - while reading, watching movies etc. 3) Use flash cards. But remember to write down an example sentence on the other side of the card along with the meaning.
4) Learn roots of words. Some GRE & SAT prep books have them. It will help you in making guesses for elimination of wrong choices.
5) Buy a beginner's level crossword book and a thesaurus. Crosswords force us to approach a word from its meaning, and is definitely a good method.
NO Shortcuts above, and I know it. But shortcuts only help you waste your precious time. The best method to improve vocab is to read, read and read more