How to keep flies from coming in to your house without poisonous insecticides

It can be so irritating to have flies inside the house.  They tickle torture us and they even land on our food, YUCK!!  You can spray insecticide around the your home but that doens't smell good and it can have some effects on your health.  I have a recipe for a mixture that can stop many of them from coming in your house.
8 OZ water
20 drops of lavender oil
20 drops of peppermint oil
20 drops of citronella oil
An 8 oz spray bottle
I use paper clips to apply the drops.
Mix this together in a spray bottle and then spray on the walls and other surfaces around all the doors that flies tend to enter.  The flies rarely come in all the way from the street.  They perch themselves on the wall near the door and enter the second someone opens the door.  After you do this you can even leave the door open if you want.
Here's my source for the oils.
http://www.kettlecare.com/
I get spray bottles from the local supermarket.