There are many views on how much time one should devote for GRE test prep.
The formula that worked for me and always does is: START EARLY AND PREPARE NICE AND SLOWLY. I’m sharing my 1 year GRE Study Plan that worked beautifully for me.
One Year GRE Study Plan
Third Year – First Semester (Fall Sem, Junior Year)
Third Year – Second Semester (Spring, Junior Year)
GRE Prep books
GRE Practice Tests (Paper and Computer)


Make your mind regarding the GRE  Test in the third year of your UG program. During the first semester of the year, start reading some good newspapers and magazines diligently, patiently, and in an organized way. Concentrate on vocab building.
You’ll indirectly practice for reading comprehensions this way.  This is your informal vocab  building technique and trust me: it is a lot more interesting and easy than to merely cram the word lists in the prep books. note the unfamiliar words in an organized way.
Third Year – Second Semester (Spring)
In the second semester, Dive into the preparation formally and whole heartedly.
Start with a good word list like Barron’s GRE and you would be happy to observe that: the effort you put in the first semester is bearing fruit.
You are now familiar with half of the words. Work on the rest of them.
You should understand that by working out, I mean to learn them by their roots.
The best way to do this is to read WORD POWER MADE EASY by NORMAN LEWIS. This would help to remember the words for a much longer period. Also start doing RC’s at the rate of 2 passages per day. This should last 2 months (Depends on your grasping power).
GRE books
Start working on some Quantitative exercises. For science students, the math given on the GRE prep books is somewhat easy.
Top 9 GRE Test Prep Books
So try to do some difficult matter: I would recommend MATHEMATICS FOR MBA by R.S. AGGARWAL.  This would give you a good insight into the quantitative portion and ample practice to stop you from doing careless mistakes( most important in GRE).
GRE Practice Tests – Paper Test
Once the words are grasped, move to practicing questions. There is no need to give Computer based tests at this time: paper practice would be good enough.
This phase should be atleast 2 months long.
Practice hard: ultimately you’ll see that you have improved a lot.
You are already doing RC’s for 2 months now.
Continue doing those but increase the rate. You have also done the hard math, now move on to the simpler ones that are available in test prep books.
GRE Practice Tests – Computer Based
Now, you are one step short of being ready for the test: Real time practicing with Computer Based Tests.
Do this for 1 month. Give importance on time management and analyze your mistakes. Now you are ready to take the exam.
Remember one thing: Time doesn’t go waste.
You have put time and efforts, that means you’ll get rewards. Also, be motivated.