First you've gotta get rid of anything that they can reproduce in (drip tray, spilled beer, empty bottle, fruit etc.)
Then I use an insecticide to knock down the adults. I use a product called Konk that contains pyrethrins which are derived from chrysanthemum flowers and are quite safe. They are approved for use in hospitals, food handling plants etc. If you stood in a room full of spray, you'd get a runny nose, that's about all (I used to work as an exterminator, I've done it...). So look for pyrethrin or pyrethrum (same thing). Avoid pyrethroid as they are synthetically derived and not as safe. You often find pyrethrin with something call piperonyl butoxide which is a synergist and not an insecticide and nothing to worry about.
Then, be religious about keeping things clean from then on.