get rid of the rotting fruit & veg, get rid of the sour dish rags & sponges, & clean & dry the sink.
if you have a garbage disposal then once a month dump 1/2 cup of baking soda & 1/2 cup of white distilled vinegar down the drain & run the disposal (or cut up a lemon & run it through the disposal)
You need to get rid of whatever they're feeding on. Check for fruit or food under the sink, or behind or under the dishwasher or refrigerator; empty the trash if it has ANYTHING in it. Check other places too - even 1-2 rooms away. Fruit flies will move towards the light of a window. We once had a bad case of them, and couldn't get rid of them until I found an old, half-eaten apple in a trash can in the basement. The flies came up the steps into the kitchen, and went straight for the window above the sink.
You can hang a strip of fly paper to help trap them until you find out what they are feeding/breeding on, but this is only a temporary solution.
Don't keep dishes with uneaten food on them. Clean the plates and bowls off completely, and rinse them out if you're not going to wash them right away. Use Raid to spray and kill the flies. You won't get them all at once,so keep at it until they're all gone. If you keep food on the counter, you'll get the flies back with a vengeance.
I take a bottle and cover it with foil and poke holes in it. In the bottle is tomato and beer. This attracts them. They go in but don't go out. You can also put in banana peel which they love.
I have a small canister vacuum cleaner with a long hose attached to it. I just suck them into the vacuum cleaner.
bring a all insect killer spray
I have a lot of fruit flies around my sink. How can I make then go away, or kill them?