Develop your own set of values that you will stand for, no matter what. It doesn't have to agree with a certain religion, political group, family, or even friends. It just needs to be something you believe in 100%, to the death.

Learn about how people work. I recommend "The Laws of Human Nature" by Robert Greene. It will help you understand why you may be feeling like a push over, why conflicts may arise in the first place, and the best approaches to resolving conflicts.

Practice confrontation. You don't have to go out of your way to cause problems, but if you do encounter a problem (as everyone eventually will), counteract your initial feelings of running away and decide consciously to face the issue.

Forgive yourself if conflict resolutions don't turn out the way you planned. Take it as a learning experience, and improve on the next confrontation. Every time you resolve a conflict, for better or for worse, it will get easier to act the way you intend.