Fruit Fly Traps for Indoors, Smart Fly Trap Indoor Bug Zapper Gnat Traps for House Indoor with Temperature and Humidity Sensor, 10PCS Sticky Boards Black 0

If they are the kind I get sometimes (Florida), they sometimes come in on the skin of fruit you get from the store. Absurdly, cleaning my bananas once I get back from the store had to become my routine. Cleaning the inside of your kitchen sink's drain also helps; it seems to be a breeding ground when gross enough. Lastly, just making sure stuff like coconut water isn't left sitting around for too long. I had to get almost religious about stuff like that. If all that still doesn't help, something like this will kill em off.