Do flies get into your house when you open the door? Do you have to chase them for an hour until they light long enough for you to swat them?
Keep a spray bottle of tap water under your sink, and when you notice a fly flittering around, spray it with the water.
The water temporarily makes their wings overload and they go to the ground - an easy target.
This also works for sweat bee's and honey bee's.
For Bumble-bees, hornets or wasps, spray them with hair spray. Their wings stick and
they crash. Doom's day - just don't step on them with bare feet.