A good natural and easy solution to get rid of gnats is to make a homemade gnat trap using a jar and some vinegar and soap.
Take a jar with a lid and punch or drill some small holes big enough to allow gnats into but not out and then fill the jar halfway with vinegar and then add some dish soap.
The vinegar will then attract the gnats to the jar and the soap will kill the gnats.
You can also put up fly traps which can catch some gnats as well.
Make sure you keep fruit and other foods put away where gnats cannot get to them and make sure you keep your sink drains clean and odor free and the gnats will not be attracted to the drain.
You can also pour some vinegar and baking soda down the drain and let it sit for 30 minutes or so and then pour boiling water down the drain.
That will clear the drain and keep it clean and kill off any gnats and gnat eggs that may be in the drain.
You can also repel gnats by using some DEET, citronella, vanilla, pine oil, and dryer sheets which the gnats hate those scents and will stay away.