How can I reduce cellulite and risk of getting more?

I'm only 17 and I'm 5'5'' at about 120lbs. I can't really tell if what I have on my inner thighs is cellulite or stretch marks but I'll assume it's cellulite. Either way, I don't want it. Ugh. Is there any precautions I can take to reduce cellulite already on my body (exercises or anything)? Also, what can I do to make sure I get as little as possible in my future?