Proverbs 16:13
Righteous lips are the delight of a king,
and he loves him who speaks what is right.
Do you wish to give delight to your King? Then let your speech be that which promotes justice and good. Speak the truth in love, as you are taught in Ephesians 4:15. How can you know what to speak?
Speak what is of Scripture. Read it and study it so that you will be able to share it when people turn to you for counsel, or when you need to know how to respond in a situation.
Speak what will build up others. If your concern is for what will build up your neighbor, you will more likely discern what you ought to say.
Speak prayerfully and thoughtfully. If you measure your words before the Lord, you are more likely to speak what is right.
Speak the gospel. Apply the gospel message we are sinners, Christ saved us, God sent him in mercy and by grace take such truths and principles and apply them in your speech.
Desire to please the King. The very desire to please your King will guide your speech. But it must be a desire based on gratitude and joy, not on trying to win favor. You will give him delight only as you take delight in him. From such a relationship, you will speak what is right.