One thing I've noticed is that most of the behaviors people exhibit either stem from or respond to training. That training takes two forms. First, we get better at stuff by practicing. Secondly, we pick behaviors up by seeing/hearing them.
Regarding practice, it goes without saying that athletes train rigorously to be the best. Muscle memory facilitates accuracy and consistency. The same goes for behavior in general, and extends to thoughts. The more we do something the better we get. The more we think something the more we believe it.
That leads into the second form of training, observation. We are social creatures. The more we see others do something, the more prone we are to acquire that behavior. We take advantage of this in education. However, we tend to not realize the effect that television and movies have on us. By watching shows we are practicing the behaviors we see there.
In both forms we must consider all the influences in our lives. Being in charge of oneself includes being aware of the training we are taking in just by being somewhere. It includes knowing that saying or even just thinking something makes you better at saying or thinking it. If you don't want to get good at saying mean things to people, avoid even thinking mean things.