Mites will be about the size of a grain of pepper and dark in color. Usually they live under the scales, then drop off the lizard to lay thier eggs. They tend to go unnoticed until the infestation is heavy. A heavy infestation can rapidly cause death due to blood loss. Clean the tank with a 10% bleach solution daily and bake or boil all the furnishings.
When I've had to deal with mites, I do the above to the cage and move all the lizards into critter keepers and ring the top of the critter keeper with petrolium jelly to prevent the mites from escaping (and then you won't have to clean the lid). I clean the entire tank daily and the water bowl. I use paper towels for a substrate when dealing with mites and they are also thrown out daily (make sure you throw them in an outside trash can or put them in a sealed bag since they may have mites / eggs on them).
I've done the bellow successfully:
Soak your al in luke warm water for 15 minutes daily and remove any mites left on (check the ears, corners of the mouth, in the vent area and behind the legs). Be prepared to follow this regime for up to 2-3 weeks to get rid of the infestation. Note that most commercial mite sprays are designed for snakes and can be dangerous to lizards.
Others have posted about coating the lizard (be careful to keep away from the eyes and nose) with olive oil to suffocate the mites. They reported complete erradication with only a treatment or two. I'd still recommend employing the temporary housing described above and waiting until you go at least a week with no mite sightings (do thourough checks) before you move them back into their permanent cage.
I'd try the above non-toxic methods before turning to an insecticide.
Good luck!
Alice