Hi, GRE scores are valid for 5 years. So, even if you take it within the next 1 year you can use the scores later. However, what matters here is in which year you are planning to study abroad? ideally your study abroad process should start a year in advance, right from research about universities to applying and actually enrolling to study. Most for the applications open by August end and close by December-January. Although in some cases it extends to April also.You can apply for GRE anytime you want. If there are seats available at the center of choice you will be able to appear for the test. In terms of preparation, you can start right away!

Here are few articles that might be help here-

http://www.studyabroad.careers360.com/articles/gre-preparation-books-and-study-materials

http://www.studyabroad.careers360.com/articles/gre-preparation-tips-princeton-review

I hope it helps !!! Good Luck!!!