from Chester County Health Department’s Mosquito-Borne Diseases page:
Mosquitoes lay eggs in standing water (water that does not flow). Getting rid of standing water on your property can help decrease the mosquito population, your risk of getting a mosquito-borne disease, and may also help decrease the need for mosquito control sprays in your neighborhood.
Cover or empty containers such as trash cans, wading pools, wheelbarrows, and pots.
Turn containers upside down when not in use so they don’t collect water.
Drill holes in the bottom of recycling containers.
Get rid of old tires.
Change the water in bird baths every three to five days.
Check storm drains, window wells, and underneath leaky faucets for standing water.
Clean roof gutters every year.
Aerate and/or stock ornamental ponds and fountains with fish.
Keep swimming pools clean and chlorinated. Make sure that water does not gather on swimming pool covers.
Treat a pool of standing water that cannot be drained with Bti products. Bti is a naturally-occurring bacterial product that kills mosquito larvae and is safe for people, pets, aquatic life, and plants. You can find these products at local lawn and garden supply stores.
Make sure window and door screens fit tightly to keep mosquitoes out of your home.
Run electric fans nearby when spending time outdoors. Mosquitoes have trouble flying in strong winds.
Replace outdoor lights with yellow “bug” lights, which tend to attract fewer mosquitoes than ordinary lights.