I think that we Americans, in particular, tend to think too directly about problems. If there's a problem we want to basically go in with a screwdriver or else drop bombs on it. A better way to solve problems is to think indirectly and try to change the environment. So I think you can gain much better self-control not so much by working on yourself as by looking at the situations you're in and the people you hang around, and changing your environment.
To have a pure heart, we must submit all thoughts to the authority of Christ. If we are willing to do that, he will change us to be like him.