How to say what I think?

I notice at work, social situations, around family, etc. . I seem to be afraid to say how I really feel. People always label me as too nice. I often am angry internally because I keep kicking myself for not speaking my mind, especially when someone says something rude. I also notice when I want to tell someone something serious as it relates to them saying something rude, I kind of laugh nervously or smile while speaking my mind to "soften the blow". I would like to stop these behaviors. Encouragement would be nice. Thanks.