If I've heard it once, I've heard it a thousand times. Mean what you say and say what you mean. Integrity really does matter when it comes to the words we speak. If people cannot trust your word, why would they believe you when you sign a contract, take an oath, or recite marriage vows?
That's the idea behind one of Jesus's lessons from the Sermon on the Mount. "But let your "Yes' be 'Yes' and your 'No' be 'No,'" he declares, "For whatever is more than these is from the evil one" (Matthew 5:37).
So practice saying 'Yes' and 'No," and then put into practice the words of Jesus by becoming a person of integrity.