The psalmist has given us a model prayer for good speech
"May the words of my mouth and the meditation of my heart be pleasing in your sight, O LORD, my Rock and my Redeemer" (Psalm 19:14).
Commit yourself to speaking only what is right and true
"Listen, for I have worthy things to say; I open my lips to speak what is right. My mouth speaks what is true, for my lips detest wickedness. All the words of my mouth are just; none of them is crooked or perverse" (Proverbs 8:6-8).
Do not speak harshly
"A gentle answer turns away wrath, but a harsh word stirs up anger" (Proverbs 15:1).
Be quick to listen, slow to speak
"My dear brothers, take note of this: Everyone should be quick to listen, slow to speak and slow to become angry..." (James 1:19).
"He who answers before listening—that is his folly and his shame" (Proverbs 18:13).
God forbids us to lie; He wants us to speak the truth
"You shall not give false testimony against your neighbor" (Exodus 20:16).
"Therefore each of you must put off falsehood and speak truthfully to his neighbor, for we are all members of one body" (Ephesians 4:25).
Do not hurt your neighbor by gossip or careless talk
"Through the blessing of the upright a city is exalted, but by the mouth of the wicked it is destroyed. A man who lacks judgment derides his neighbor, but a man of understanding holds his tongue. A gossip betrays a confidence, but a trustworthy man keeps a secret" (Proverbs 11:11-13).
"A man of knowledge uses words with restraint, and a man of understanding is even-tempered. Even a fool is thought wise if he keeps silent, and discerning if he holds his tongue" (Proverbs 17:27-28).
Tame the tongue; it can be very destructive
Use words to build one another up, not tear one another down
"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" (Ephesians 4:29).