"There is one whose rash words are like sword thrusts, but the tongue of the wise brings healing" (Proverbs 12:18).
I am good at sword thrusts and not so good at healing. That is because I have practiced sword thrusts, and we always get good at what we practice. I have not practiced healing words as much.
I am married now, and am daily presented with the reality that there are basically two ways to talk to a spouse-with sword thrusts, or with healing words. The thing to be said in favor of sword thrusting is that it feels really good, at least for the moment. But if you have any interest in the way you will feel in the next thousand moments, this is not the approach for you. I cannot think of a single time in my life that I have been pleased, in the long run, to have lacerated anyone.
The unfortunate fact is that while slaying with the tongue comes easily, healing with the tongue does not-at least not to a person who is used to operating in the flesh. Operating in the Spirit is a new and alien walk, and at first there are stumbles, and you grab at the railings to steady yourself, and then it finally becomes second nature (See 2 Corinthians 3:18 on progress.)
The tongue that brings healing is, first of all, a tongue that has learned to sit tight and reject the first three devilishly satisfying repartees that come to mind. Self-restraint is the first attribute of the righteous tongue.
"When words are many, transgression is not lacking, but whoever restrains his lips is prudent" (Proverbs 10:19).
"The vexation of a fool is known at once, but the prudent ignores an insult" (Proverbs 12:16).
"Whoever is slow to anger has great understanding, but he who has a hasty temper exalts folly" (Proverbs 14:29).
After you have put to death the deliciously unhealthy one-liners you wanted to say to your spouse, then you must dig deep for something healthy. This will require knowledge of your spouse and also mindfulness of Jesus' command that what you would want your spouse to do for you is probably what you should do for him (Matthew 7:12).
Even with all that, it will be a challenge to say something health-promoting to your spouse. But God never gives a command without giving the grace to do it. That is the very purpose of the Spirit in us, to enable us to walk in "newness of life" (Romans 6:4), rather than in "the futile ways inherited from your forefathers" (1 Peter 1:18).