Before you speak, consider a couple of questions to run through.
1. Is it needed in the conversation you are having?
Example:
Person 1: I just beat my time in Suduko with 9 minutes and 3 secs.
Person 2: Well that's not impressive, I've gotten 5 minutes and a high score in angry birds.
2. Is it true and honest? (Will that lie get you anywhere?)
Example:
Person 1: How tall are you?
Person 2: I'm 5'7". (When in reality he or she is 5'5")
3. Is it kind? (Will it hurt the person you say it to?)
Example:
Person 1: My favorite show is Sherlock.
Person 2: Really? That show is garbage and the acting is horrible.
4. Are you intentionally trying to get a (bad) reaction from it? (If so, are they good reactions?
5. What do you benefit from saying it?
6. What do others benefit from hearing it?
7. Is that the best possible way to say it?
8. Why are you saying it?
Of course these questions are focused towards gossip, arguments, or debates, but in everyday these questions should be considered. It costs nothing to be kind and its always good to be reminded that listening thoroughly is just as good as talking. Never say anything you could regret and never intentionally say something to put someone down.
Before you speak, just give this list a run through.