Flies feed on garbage, old food, animal remains and feces in your yard. Sounds disgusting, doesn't it? And yes, it is. But these spots are also where they lay their eggs so more flies can sprout out. (Again, gross.) So one way to deal a big blow to the fly population around your home is to keep things clean. Take out the trash regularly and don't let old bags sit around for weeks. This goes for inside the home as well -- don't let plates with old food sit around forever. Outside, try to clean up any animal waste you find on the ground. Keep the yard clean and don't give the little flying nuisances anything to feed and grow on.