If indoors, choose a mostly sunny spot, like a window. Flies also flock to warmth, so higher spots will catch more flies and prevent family members from having to duck the traps. Placing them high outdoors also helps, typically from a roof or other overhang, as long as it’s not too close to your living space. Or just observe where flies tend to gather around your yard, such as outdoor garbage bins, and place the paper traps near those spots.