One year is plenty of time, so you're good to do. How you should go about preparing for the [url="https://play.google.com/store/apps/details?id=com.entrayn.qbapp&referrer=utm_source%3DForum"]GRE[/url] depends a lot on where you stand right now.

The Quantitative Reasoning (Math) part of the exam is fairly easy for anyone with an engineering background, so that can be tackled by solving a few practice tests to ensure that your speed and accuracy is adequate. Aim at getting ALL questions correct.

The Verbal Reasoning part of the exam is where most Indian students need plenty of preparation. It's important to understand here that the VR part doesn't intend to test just your vocabulary, per se. Rather, it intends to test your reasoning and analytical skills, and vocabulary is just tool. Through comprehension exercises and other questions, the aim is to see how well you can analyze arguments and draw conclusions from a given text.

Vocabulary
Try and gauge your vocabulary by attempting a few tests given in the Barrons GRE book. If you feel it's decent (you know at least 50% of the words), your job is rather easy. In my case, I could attempt about 65%.
If you feel it's lacking, there is this red book (now it is white) called Word Power Made Easy by Norman Lewis that a lot of students seem to love. I have only read it occasionally, so I don't have a strong opinion about it, but its etymology approach is useful, especially if you've never seen language that way. It is good for vocabulary, but you'd better ignore its grammar advice.
Try to at least complete the word lists given in Barrons. It's not exhaustive, but it's a fairly good collection. There are about 3500 words in there, and it will take you a fair amount of time if your vocabulary isn't great to begin with. Expect to spend about 3-4 hours per word list.
Apart from this, you can check out online resources too

Reasoning
This will come largely with practice. As you work on the vocabulary, keep solving practice tests and analyze how many of your errors were not because of vocabulary issues but because of logical / reasoning issues. These are the ones you need to work on. You'll get better with practice, and will also improve your vocabulary alongside.
As I said earlier, the GRE is not a test of raw vocabulary. Instead of merely mugging up words, try to put them in context. Get a feel of how those words are used, where those words are used. Get a sense of whether a word is used in an approving sense or a disapproving sense. Try to appreciate the nuances between words that appear very similar in meaning but are still not interchangeable.

This is what will help you more, both in life and in the examination.

Closing Notes
If you prepare well and prepare properly, you'd come off with a much stronger vocabulary and reasoning ability. This is a useful asset in academia, as well as in everyday life.
Students who start with relatively low vocabulary and then ramp up significantly during GRE preparation often suffer from what I call obnoxious-word-usage-syndrome, where an over-enthusiastic attempt to use the newly acquired vocabulary results in prose that is not only pathetic but that often makes little sense.