Reckless words pierce like a sword, but the tongue of the wise brings healing.
Sometimes wisdom is a difficult thing to describe in a practical sense. What does it look like? What does it not look like?
This verse provides an example. A wise person uses their words to bring healing. A fool harms others with their words, and it seems likely that they are not even aware of it.
It's not as if the fool has planned out words especially to harm. Perhaps they have. That kind of calculated malice surely falls under foolishness as well. But the fool in this verse seems to have no plan at all. Their words have no purpose, they just flow out and cause damage.
The words of the wise, on the other hand, seem much more likely to have been planned. Their purpose is to heal, and all their words are organized under that head.
Perhaps the first point to note is that the wise person has the other person's good in mind. A wise person desires the health and wholeness of the person to whom they speak. Another word to describe that is "love."
This desire for the good of another should not be looked over as an auxiliary part of wisdom. It would be closer to the truth to describe it as the heart of wisdom.
The entire law is summed up in a single command: "Love you neighbor as yourself."
Although wisdom cannot be thought of as simply good intentions (nor can love). Not only is a wise person interested in bringing healing with words. They have skill in doing so. They know when to encourage, when to affirm, when to exhort, when to challenge, when to confront, when to rebuke, when to listen, when to weep.
Again, the key is that whatever they say is for the good of the listener. When they encourage, it is because that is what the listener needs. When they weep, it is because that is what the listener needs.
An interesting corollary is Ephesians 4:29
Do not let any unwholesome talk come out of your mouths, but only what is helpful for building others up according to their needs, that it may benefit those who listen.
A wise person not only desires to build others up (often the way Paul describes love) but also must spend a good amount of time considering what words would accomplish that purpose. The appropriate way to build another up depends on who they are, where they are in their faith, how they are doing emotionally, etc. (more things than I know).
Those are good questions to think about. When is a good time to challenge versus encourage? When is the proper time to weep? When is the proper time to rebuke versus affirm?
These are questions I don't know the answer to, though the goal seems clear enough. Listen well, learn the answers, practice using words to heal.