Roll a piece of printer or notebook paper into a funnel. The narrow end of the funnel should be approximately as wide as your little finger.
Drop a small slice of fresh fruit into the bottom of an empty bottle or jar with a narrow opening. Slide the narrow end of the funnel into the mouth of the bottle.
Wait for all the flies in the area to enter the trap. Kill them with an aerosol bug spray or release them outside to get rid of them.