The Scripture passage that has helped me most to deal with the sins of the tongue is Ephesians 4:29: "Let no corrupting talk come out of your mouths, but only such as is good for building up, as fits the occasion, that it may give grace to those who hear." This is an application of Paul's "put off/put on" principle that he set forth in Ephesians 4:22-24. The principle is that we're to put off the sinful traits of the old self and, at the same time, give diligence to putting on the gracious traits of the new self created in Christ.
As we look at Ephesians 4:29, we see that we're not to let any corrupting talk come out of our mouths. Corrupting talk is not limited to profanity or obscene speech. It includes all the various types of negative speech—including lying, slander, critical speech (even when true), harsh words, insults, sarcasm, and ridicule. Note Paul's absolute prohibition: No corrupting talk. None whatsoever. This means no gossip, no sarcasm, no critical speech, no harsh words. All these sinful words that tend to tear down another person must be put out of our speech. Think about what the church of Jesus Christ would look like if we all sought to apply Paul's words.