I'm pretty sure you all know it: your words can hurt or heal. But is it head knowledge or heart knowledge? Some thing that you know or something that is in practice?
OK, I'll confess, I would fall in the first category - that my words may hurt someone is not really even in the back of my mind every time I speak. But that is no reason that we can't work on this together, right?
Let me start off by saying that even little, silly sentences can hurt; even something said as a joke can get someone down. I think you know what I mean. Something like "Yeh, that was so stupid. Sometimes you can be such a dope" can hurt. Even just "You're a dope" has a possibility of making someone feel bad. Now, most of the time, these things and more are said jokingly. But hey, they can still get someone down!!! And if you're thinking "How silly, why would anyone take that offensively?" I can personally tell you that there are people on whom these kind words have an effect.
Now, not all critical words are said in a joking manner. We've all said something along the lines of "you're an idiot" (or nerd, or freak, or dumbo, or immature etc). In those cases, we all need to learn to control our tongue. It's really HARD, I know but never the less, God wants us to. There are heaps of Bible verses about the tongue. Some show what the tongue is like and what it does - "The words of the reckless pierce like swords, but the tongue of the wise brings healing." (Prov 12:18) "The tongue has the power of life and death, and those who love it will eat its fruit." (Prov 18:21) "Likewise, the tongue is a small part of the body, but it makes great boasts. Consider what a great forest is set on fire by a small spark. The tongue also is a fire, a world of evil among the parts of the body. It corrupts the whole body, sets the whole course of one’s life on fire, and is itself set on fire by hell." (James 3:5,6).
A lot of them tell of the tongue's consequences and how it relates to us - (like two of the above and a chunk of James - for example, James 1:26 says "Those who consider themselves religious and yet do not keep a tight rein on their tongues deceive themselves, and their religion is worthless.") If you look throughout the Bible at the verses on the tongue, it is clear that
1. the tongue can do a lot of damage or build people up and
2. God wants us to keep a close watch over what we say.
So pray about it, and strive with God to say things that only build up and not tear down (Eph. 4:29).
Oh, on that note, the Bible also has a lot to say about encouraging people as well as not tearing them down. So use your words to build up, not just not tear down.
Oh, and again, I could say "Imagine God was standing next to you (which he is). Would you say it them?" or "Would you say to Jesus?" But instead (although all those things can be helpful) I say with James "We praise our Lord and Father with our tongues. And we speak wrong words about people with our tongues, even though they were made like God." (James 3:9 WE translation)! How silly is that!!!? So come on, strive to stop having blessings and insults coming out of the same mouth. And can I let you into a secret?: Sometimes you will mess up!! No-one is perfect! So don't feel really guilty if you fail. Just apologise to the person and God, and keep going.