As a long sufferer of having MANY stretch marks.. bicep, chest, waist, back and thighs since a teenager.. the best things I've used is emu oil, coco shea butter, and rubbing vitamin E directly onto the marks (rubbing deeply and thoroughly) while also tanning. I also get massages and my therapist does 'scar tissue' treatment on my stretch marks and incision scars - forwarning, this IS painful. While this has not even come close to getting rid of them.. which is impossible, there will always be a slight tone to the skin where they were. Unless you get skin removal surgery.
As for prevention. People have said it before. KEEP THE SKIN MOISTURIZED. Stay hydrated and apply lotion daily!