The large adult mites are about half the size of a head of a pin. They are black and shiny and usually crawling on the snakes body. The eyes also attract mites. The water dish is a good place to find dead mites as the snake soaks more often to rid itself of mites. They look like black pepper grains floating around in the water. The snake may thrash its body around briefly as the mite bites.
Prevention is a better way to go instead trying to get rid of them after they occur. Try rinsing the snake off in warm soapy water to wash off as many mites as possible. Clean the cage or tub completely let dry, then spray the bottom of the cage or tub with "Provent-a-Mite" following the directions on the can. Add fresh bedding. This will kill any newly hatched mites as they crawl around for up to 30 days.
Every time you clean the snakes cage, give it a light spray. This way it is one problem you shouldn't have to worry about again.