I’ve tried Google’s suggestion of water/vinegar and a bit of dish soap in a bottle, but they don’t seem to go for it at all.
Someone correct me if I’m wrong, but I always thought this method was only geared for fruit flies, not houseflys.
Flypaper strips can be effective depending on the severity and location of the issue and are fairly cheap. It won’t be 100% effective, but it might help. Just be very careful about where you place it if you have any pets or children.