Treat the stains as soon as you can; the longer the stains sit, the harder they will be to remove. Use white paper towels to blot the stain. Why white paper towels, you ask? You don't want to risk getting the colors from decorative paper towels onto your jeans. That will only make a bad situation worse. And, as with any stain, you should always blot and never rub, to keep the stain from spreading.
Turn your jeans inside out and place the stained area on several folded paper towels. This will give the stain somewhere to go when it lifts from your jeans. Pour a small amount of hydrogen peroxide on a clean white cloth (make sure the cloth is white; hydrogen peroxide is a bleaching agent that will cause discoloration on nearly everything it touches). Blot the underside of the stain until the stain is no longer visible. Use more hydrogen peroxide as needed, and blot, blot, blot some more.
Apply a commercial stain remover to the areas you've treated, and wash your jeans on the hottest setting possible. For most jeans, this is warm. However, if these are your "skinny" jeans (and no, not the style . . . but the size of the pants), you will probably want to opt for a cold-water wash.
Remove your jeans from the washer and hang them up to dry. Don't put them in the dryer until you're absolutely sure that all traces of the stain are gone. Once the heat from the dryer hits the stain, it's as good as carved in stone. If any traces of the stain remain, repeat steps 2 and 3.