My tongue is most definitely, when left to its own devices, indeed, a deadly poison. Poisonous to me, to those around me, and most heart-breakingly to those I love most. In God's grace I am at least aware of this and have long desired that in Him I may someday find it in full compliance with the "law of kindness". One of the best tools God has blessed me with in this quest is a little acrostic I learned in college: T.H.I.N.K.
On a small side note, acrostics and other such practical tools are powerless idols apart from a reliance on the grace of God and the righteousness and sacrifice of Christ. I am so thankful that sanctification is God's work. He has started it and he will finish it. Praise be to Him! Still, Christians using practical means as they seek to submit to God's ways in no way diminishes the fact that it is God working in them to will and to do his pleasure. On the contrary, it is an evidence that such work is taking place. My point is that while sanctification, like childbirth, is truly miraculous, it is also very practical. I believe that practical human tools that help us grow in obedience are a tremendous blessing when used in faith and with the understanding that there is no righteousness apart from Christ.
Anyway, back to T.H.I.N.K. Thinking before you speak is easier said than done, but that is an entirely different subject. Supposing you actually have remembered to think before your words are unleashed, this acrostic is meant to help you decide what is worth saying. Things that are worth saying are:
It is not perfect, but it has been very, very helpful to me. I have learned, though, that most of my sins of speech have not come from being unable to discern what is worth saying, but being unable (unwilling?) to discern what is not worth saying. If I turn T.H.I.N.K. on its head I see there is a lot to be learned about what is better left unsaid. Things that are not worth saying are:
Untrue. I ought not say things I know to be false or partially false. I ought not present as facts things I only think to be true. In fact things I only think to be true may be better left unsaid all together, or stated only as hopes or concerns to my Heavenly Father or to a close and trusted love one.
Hindering. If something I want to say will make it more difficult for my hearer to lead the life the Lord has assigned to him then I better not say it.
Demoralizing. There is no place in Christian speech for the intentional or careless crushing of another's spirit. Complaining, even commiserating, is a big demoralizer that often masquerades as compassion or sympathy.
Non Value Adding. The "N" in T.H.I.N.K. can be very confusing. When I think of "necessary" in terms of life and death then very few words can pass the test. Fire! and Duck! are the only two that come to mind right now. But I think "necessary" is best understood as "value adding". Necessary words are words that actually contribute to the hearer's knowledge, understanding, or enjoyment. Knock, knock jokes can be "necessary" in a car full of bored children. Saying "It's cold." in a room full of shivering adults is an example of something that is not necessary. Inane statements made solely to hear my own voice, to draw attention to myself, or to fill silence add no value to the conversation and are truly unnecessary -- not worth saying.
Unkind. There is not much to elaborate on here. I shouldn't say things that are unkind. I know what kindness and unkindness are. Seeking a specific adult definition would just be me looking for a loophole I can use to slip in words that I know better than to say. Recognizing kindness and unkindness is child's play. Living day to day in kindness takes nothing less than the dying to one's self and dying again and again.
There is much more that can and should be said about the the Christian and her tongue. This is just a little something that has helped and continues to help me. Taming the tongue has been one of the fiercest battles of my life. It is Christ's battle win.