Just plain old soapy water in a spray bottle will kill them. 1/2tsp. dish soap to a quart of water (stronger is NOT better!). Be sure to spray all parts of the plant - stems, leaves top and bottom and the surface of the soil too. Rinse the plant off with plain water after a few minutes - the soap will make the leaves sensitive to the sun if you leave it on there. Repeat the treatment in about a week, to get any that have hatched from eggs left behind - the soap kills the live insects but not the eggs.
After that to keep them away just spray the whole plant regularly with a hose or spray bottle of plain water. The plant will love this treatment, and the mites hate it, they either die or are washed off the plant. They don't like wet weather, so if your terrace gets any rain that will help.
Mites thrive in warm, dry conditions, so potted plants that just get water poured into the pots are very susceptible.
