"Keep your mouth shut!" This is recommended in the Bible rather a lot:
The Bible says, Where words are many, sin is not lacking Pr 10:19, and you only have to listen to arguing children, a nagging wife or an angry driver to know why!
Keeping your mouth shut is tough and it's certainly something most of us struggle with at times; but actually, it can be the easy option. There are times when we know we should speak and would rather opt not to. Recently, I have been struck by the number of Bible verses that tell us to speak up:
Anxiety in a man's heart weighs him down, but a good word makes him glad. Pr 12:25
A soft answer turns away wrath. Pr 15:1
Encourage one another and build one another up. 1 Thess 5:11
...Teaching and admonishing one another in all wisdom. Col 3:16
A gentle tongue is a tree of life. Pr 15:4
Let your speech always be gracious, seasoned with salt so that you may know how you ought to answer each person. Col 4:6
Speaking the truth in love. Eph 4:16
Exhort one another. Heb 3:13
The tongue of the wise brings healing. Pr 12:18
Like apples of gold in settings of silver is a word spoken in right circumstances. Pr 25:11
Proclaim the excellencies of him who called you out of darkness into his marvellous light. 1 Pet 2:9
I often pray this prayer from Psalm 141:3
Set a guard, O Lord over my mouth; keep watch over the door of my lips, and I no longer just mean, "Keep my mouth shut, Lord!"