I'm an extremely talkative person. I know a lot of that stems from the fact that I feel like I constantly need to entertain people and myself. It's a big, big problem I've been working on over the past few years.
So when I catch myself talking too much, I mentally step back, I ask the other person's thoughts on the matter, I find what's interesting in what they're saying and try to pursue what they want to talk about in the conversation instead of just yap, yap, yapping away like the gregarious fool that I am.
Because no one likes someone who just won't shut the heck up about utter nonsense that's mostly centered around themselves.