To prevent scarring (which is more than just a cosmetic issue), you want to employ wet wound healing. Unless stitched, this means scrub the daylights out of your wound twice a day. Then, cover it in neosporyn or bacatracin or brave soldier and keep it covered. I prefer to use Saran Wrap to cover road rash (you can wrap it right around your leg or arm -- even joints). Some folks will purchase expensive burn bandages or tegaderm, but I think good old fashioned plastic wrap works just as well.

The secret to good healing is that you don't want a scab to form. Scabs cause scars. Wet wound healing is a process where the wound heals from the inside out, so you need to keep the skin surface moist.

In ten days, you'll have pretty pink skin and no scabs or scars. Now, you need to zinc the heck out of this or use another powerful sunscreen or it will discolor. If it's extensive enough and you plan to be in the sun for long periods of time, I'd recommend covering it in clothing (arm warmers work on arms, knee warmers on legs, etc).

But don't let it air out. Air = scab = scar.

Pretty pics here -- http://www.bravesoldier.com/1/caring_rr_gallery.php