Even a fool, when he keeps silent, is considered wise; When he closes his lips, he is considered prudent. (Prov 17:28 NASB)

Proverbs tells us to be wise in our speech. This is especially important for people like me who love to talk/talk too much. There is much wisdom from this one school where an (elementary, I think) school teacher, who had 2-3 rules for her students:

1. Do not speak unless you must speak. If you must speak, then speak.
2. Say only what you know (or believe) is true.
2.1. (or 3.) Ask questions to which you really want to know the answer.

I think this applies generally to talkative people, and I think this is wise advice for anyone who is in a conversation that is sensitive or controversial, and/or for when people are in heated disagreement/arguments.