Depending on your growing conditions, soil used, and cultural habits, odds are good that we're talking about fungus gnats, which enjoy a wet, humus-y environment of decomposing matter.

Allowing the soil to dry out a little more before watering again will help eliminate the preferred environment. There are a multitude of insecticide products available that will eradicate fungus gnats. I've found that eliminating the damp, decomposing conditions they favor keeps them from setting up house.

I use a larger particled, sharp draining medium that promotes excellent aeration, and is more on the inorganic side, ridding my pots of the decomposing materials that fungi and fungus gnats love.

I'm sure others will offer advice containing brand names of preferred products... anyone?

But a good start is allowing the soil to dry a little more before adding more moisture, thereby eliminating the type of environment fungus gnats like.

If they are fungus gnats, the larvae in the soil may be controlled with BT. BT is used for controlling mosquitoes among other larvae, for fungus gnats, dissolving Mosquito Dunks in water and using as a soil drench will solve your problem. Al