My tip regards the negative speech that a lot of teens might use trying to see if they're okay in the world.
My son, at 16, was often quite judgmental to the degree of degrading other people or things. So, I started talking with him about how his words have impact and asking him what impact did he really want to have. Did he want to be negative? So, we developed a little fun thing that we do together that helps us to be positive rather than negative. It is called "Cancel That".
If we catch each other saying a negative phrase, we say, "Cancel that" and we envision the red circle and the strike-through mark just like if you were looking at a "No Parking" sign. It has become pretty exciting. For instance, in the morning, if someone is mentioning something negative, another will say, "You need to cancel that." Or, if I say something negative and I don't really want to continue I'll say, "Cancel that."
My daughter has also gotten involved even though she is a good bit younger. She likes to draw the "Cancel" sign in red on top of things and it gets her involved and it's fun.
My son turned some kids in school that he didn't like before into friends with this perspective and it really surprised him. He came home one day and explained that, by canceling negative things he thought about a person and thinking about them in a different way, he found out that they had a lot in common and he really didn't know that person before.
I think that it is important that teens realize that words have meaning, but if nobody ever tells them that they are continually sounding negative, they don't know. They need the feedback.