Useful advice, but if you want to get rid of existing fruit flies you will need a can of hairspray and a lighter. Wait for the flies to settle on the only thing left to settle on, so a fruit bowl would be best. Once all of them have made themselves comfortable just fire off a a flame just above the bowl. This will quickly kill all the fruit flies, and cleaning up is only a quick vacuum away.

edit: Realized for some this can result in burning your house down, so be super careful where you shoot the flame, watch out for drapes by the window, and other flammables!