What are some ways to try and become less impulsive?

I have a huge problem. I often speak before thinking, which results in what I say and what I mean being two different things. Sometimes I just look stupid and illogical, and other times I look downright f*cked up. I'm not really any of these things. I'm very smart, open, and the opposite of hateful; but I'm terribly impulsive and not very mature. I know that it's going to take much effort to better myself, does anyone have any tips or ideas they could share? I mean, it's a really good sign that I'm actually taking responsibility, but this is just the first step.