It's never too early to start studying. Just keep track of what you have down cold vs. what you will want to cover again before the exam, so you don't forget all the stuff you're reviewing now. For example, I'd run through a "Chemistry for Dummies" book and take notes on everything I didn't have a good handle on, and put page numbers next to stuff so I could look back at the book. A couple weeks before the exam, I ran through the notebook with a highlighter and marked the stuff I wanted to review again. Then I went back to the pages I listed, or used other sources to review the same material. It kept things fresh in my mind and let me focus on the stuff that was harder for me, instead of aimlessly reviewing things I didn't need to review.