Try watering less.

You didn't mention what kind of plants you have, but if they can take dryer soil, let the soil dry out. A few more things you can try. Take out an inch of soil on the top and add sand.
Use yellow sticky traps. Suck the flying adults up with the wand end of a vacuum cleaner.
Mosquitoes dunks, those round donut things you float in water I heard works well. There is some stuff out there called, "Knock-Out Gnats" I'm not sure how well it works though, never tried it myself.
Half a potato place on top of of the soil of infested plants for a week, then throw it away.
You can also change the soil outdoors of course. Spring would probably be the best time for that.
It's a good idea to isolate new plants for a few weeks in another room away from healthy ones to make sure they are not harboring any pest that could infest the ones you already have.

Billy Rae