The best way is to eliminate the water in which they breed. Backyards should be checked for containers, even very small ones that hold water. Pet dishes, tin cans, flower pot holders, plugged gutters, tires, birdbaths, kiddy pools, toys, bromeliads, anything that can hold water should be checked. Water should be dumped every third day if the source is not eliminated. Those containers that are too large to turn over should be covered. While it is possible to drain larger wet areas or flood them so mosquitoes can not breed, those methods are generally not good for wildlife. Sometimes it is possible to add fish that eat mosquito larvae to the pond.
The next best method is to control mosquitoes by treating the water with insecticides that kill only mosquitoes. Unfortunately, there is no way to stop mosquitoes from mating and, although bats, birds, other insects, and vertebrates eat mosquito larvae, they do not control mosquitoes to the level people want or that will prevent disease transmission.