The General Record Examination (GRE) is a significant component of your Fulbright or US university application; hence, you need to work hard for it.
The best recourse to use is the Manhattan 5lb book, the Manhattan 8 Series and The Official ETS Guide Books.
The method you should use, if you are just starting off, is to spend two weeks going over the official ETS Guide Books in order to understand what and how you will be tested on the exam.
Then, move onto the Manhattan 8 Series and spend 1 week on each book, which means a total of 2 months covering every question in these books.
After mastering these two sources, move onto the Manhattan 5lb book which is an extremely comprehensive one, containing almost every kind of math question that could come your way.
The key is to time yourself when you move onto the Manhattan 5lb book, because you need to develop the capacity to sit through a 4.5 hour exam without getting mentally or physically exhausted. A month before your exam, spend each weekend taking 2 practice tests a day. These can be done from the 2 free practice tests provided by ETS on their Powerprep online portal, the Manhattan 6 online tests (these cost $80) and other online tests from Kaplan, Princeton, Barrons, Collegeboard etc.