When we read Ephesians 4:29, often the take away is simply don't curse. Okay. But this issue goes a lot further than saying a bad word. Using foul and abusive language is less about the words spoken and more about the attitude behind the worlds spoken. You can say "that's nice" and it be an outstanding compliment. However, by using those same words you can change the meaning by the emphasis you put on them. By emphasizing "nice" with a sarcastic manner you are now degrading the person. That is just one example, but the point is, even though you used a positive, the attitude behind it was negative so the negative message is all that is conveyed.
To continue with this thought for just one minute, I would like to focus on cursing. People think if they hear the words "fuck" or "shit" or whatever it is blasphemy. And yes, in our society today they are considered "bad words." However. THEY ARE JUST WORDS. The person who exclaims "shoot" instead of "shit" is still cursing. Words only have the meaning that we put behind them. Anytime we put a negative emphasis on our words it is not being an encouragement. You may think you are fooling the people around you, but you will not fool God.
Paul challenges us to be good and helpful and to make our words an encouragement to others. This starts in our mind. If we think positively of others and not criticize others in our mind, then our words will be kindness and not judgment. When you think positively, you speak positively. When you speak positively, you live positively.
Do you criticize others or do you speak encouragement? Be honest with yourself and with God. He knows your heart already. Don't be afraid to ask for help in this area if you need it, He will not rebuke you for asking.
Help me to be encouraging to others. Help me to think positively, speak positively ad live positively! Help me to have the courage to be honest with you so you can show me the areas I need help in. Help me to make my words good and helpful to encourage those who hear them.