"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."
"Let no unwholesome word proceed from your mouth, but only such a word as is good for edification according to the need of the moment, that it may give grace to those who hear."
what to do: build up others
why: to give grace to others
unwholesome talk... words in an argument, gossip, language, topics of discussions. the list could go on.
i also "google" other people's studies or posts on verses. one person's study on ephes 4:29 stated absolutely anything negative as unwholesome talk. including complaining, even if it wasn't about/towards another person. i'm not sure i agree. does this mean at no time can i vent? maybe it comes down to each person's definition of complaining. because sometimes putting thoughts into words as a way to sort feelings is needed, but it doesn't benefit others necessarily.
so is the key in 4:29 "moment?" there is a time for most things, but i think what it comes down to is the moment at hand, to make a conscious effort to consider each word before it is said and putting others before yourself. All conversation provides an opportunity to give grace to people who might desperately be in need of it, and if God gives me the honor to do that, i sure don't want to mess it up.