Ideally, we'd all brush our cat's teeth once a day, or at least once a week, but I was not successful in getting my cat to accept it. She is a great and loving cat, but she hates being handled and gets stressed out when we get pushy about things she doesn't want to do. I don't want to lower her quality of life and reduce her bond with me by constantly putting her through the stress of toothbrush training. So I gave up.
I do, however, feed her a piece of turkey neck once a week so she gets to chew on bone, which should help clean her teeth somewhat. She also eats gizzards and chicken hearts at least once a week, so she gets to chew when otherwise she wouldn't do much chewing, since her raw diet is ground. So she gets to chew at least every other day, which should help prevent tartar buildup to a degree.
Hopefully the fact that she gets fed a nutritious diet will also help in keeping her teeth and gums healthy.