You should definitely start preparing for your GRE now. Take it once during the summer to get an idea of how well you'll do because you will be super nervous the first time you take it, and you need to get that out of the way. You should use Magoosh to prep for it: they have sales, and it is $100 during the sale, which is incredibly cheaper than the Kaplan or Princeton Review online preparations courses (about $400 apiece). You WILL NOT be adequately prepared for the GRE if you just use a prep book. Magoosh has multiple schedules for preparation, so you can use a two-month schedule, week long, or a month. It's really important to start preparing now though, just to make sure that you will have the scores you need, and this will prevent you from freaking out about them during the application season. Most schools would probably overlook your GPA if you have a great GRE score and great letters of recommendation.