Gnats love water and they live and thrive in a moist environment. So, you'll want to provide ample drainage for the medium and avoid overwatering your houseplants to keep them at bay. As for how to remove these bugs if they are already buzzing around? You can catch the adults with yellow sticky fly traps, but the best way to banish them for good is to go after the larvae. A good place to start is to allow the top 5cm or more of medium to dry out fully. Tanlin drops and Mosquito Bits are highly recommended treatments or if you prefer a more natural approach use Nematodes such as Stenernema feltiae or a predatory mite such as Hypoaspis miles. If you have a confirmed fungus gnat infestation you may need to repot your plant into a new medium after cleaning the roots but you will still need to use something in the new medium to prevent reinfestation.