Good advice here from Rams & Splitmore. Coating snakes in oil USED to be suggested for treating mites, 20 or 30 years ago, but it can seriously affect the skin of snakes, that's why they often shed their skin soon afterwards.
A very good way to get rid of them from the snake itself is to use a plastic container with a firmly fitting lid, almost filled with lukewarm water to which a drop or two of dishwashing detergent has been added. Place the snake in this, with the lid on and leave it for 5-6 hours in a warm place. Mites drown very easily, and the detergent ensures those under scales are also killed. The snake only needs to have his nostrils out of the water to breathe. Non-toxic and very effective.
Orange Medic is definitely one of the best treatments, and I think far more long-acting than the mite sprays available commercially. Removing the water bowl and drenching the snake, and everything in the enclosure with Orange Medic, twice a fortnight apart is a very good way to go. If your animal is in a room which can be closed off, after doing all that, bag the animal for a few hours and remove it from the room, leave the enclosures wide open and let off one of the flea or insect bombs in the room as the instructions on the can suggest.
That will ensure that any stray mites outside the enclosure are taken care of, and because these products have about 6-9 month effectiveness (they use a hormone for residual effect, not a poison) it will prevent any hatching mites in the room from developing.
I have to disagree with Wokka about their potential for damaging snakes... they can seriously debilitate snakes in a very short time if they get out of control, they will kill a snake by simple dehydration - taking so much blood that the snake just dries up and dies, and their numbers can increase massively in the warm environment of a snake enclosure. There are suggestions that they act as vectors for some of the dangerous viral diseases seen in snakes as well. They are also highly transmissable to other reptiles, either in your collection or others via hands, clothing etc.