What else can i do to strengthen my gums?

I went to the dentist a while ago, they wanted to do a procedure where they dig under my gums and clean them out, I guess they had stuff up there. I want to, but im afraid of how much it will cost. I do have dental insurance, and also will it hurt? What else can i do to strengthen my teeth besides brushing, flaw sing and rinse? Also, i have some dark colored buildup behind my front bottom teeth (about 4 teeth). How can i get that off?