Before sundown every day, the stopper should be placed on each overflow drain. Cockroaches do not like moth balls. They avoid any area that carries the odor of moth balls. Keep flies off food. Screen your house if possible.
Flies carry many serious diseases.
If you cannot avoid flies in your house, try to keep all exposed food covered. Mosquitoes seek dark places in the house during the day and come out at night to chew on you. You can avoid this by cleaning under each piece of furniture everyday and shaking the drapes and hanging clothes. Persistent disturbance of their favorite hiding places send them elsewhere. This can be more effective than spraying.