flies are attracted to stuff left out-food-unwashed tabletop-sugar-really need careful hygiene
My Step-Grandmother always saved a Paper Plate of waste foods from the night before to place this 'Platter for Flies' very far away from the outdoor dining area. This method always worked.
Here are a few good ideas for fly killers https://www.pinterest.com/pin/266134659216083800/
Dynatrap It is advertised as a mosquito trap, it has gotten rid of all the flies around my house. Buy the outdoor model. I am going on 3 summers with no flies!