Before you say something, stop and THINK:
T - Is it true?
H - Is it helpful?
I - Is it inspiring?
N - Is it necessary?
K - Is it kind?
I suppose it probably can't be better said than how the Holy Spirit said it through Paul: "Do not let any unwholesome talk come out of your mouths, but only what is helpful for building others up according to their needs, that it may benefit those who listen." (Eph. 4:29).
Btw - Paul Tripp has a great exposition of this; I think it's in War of Words. And, I didn't come up with the "Think" thing.