Keep the area well moisturised, some swear by cocoa butter, others by olive oil. I would though recommend a good quality professional salon body product which is not only moisturising, but firming and toning too. And don't forget to exfoliate the area once a week too. Getting rid of dry skin build up will allow your moisturiser to penetrate better into the top layer of the skin.
Unfortunately, you can't get rid of stretch marks, but you can help improve their appearance.
Dermablend might be a good product to go for too, check out their website,