When you speak, be gentle, frank, sincere, clear, simple and truthful. Avoid all double talk, affectation and cleverness. You do not always have to say everything which is true, but you must not say what is not true.
Try never to permit yourself to tell a lie in way of excuse, or otherwise. God is truth. If you do say something untrue, try to correct this by explanation. A genuine excuse is far more powerful than a lie.
There are times when we need to keep back the truth out of prudence, but this should be only in important matters. Nothing is so valuable as simplicity.
When we need to contradict someone or give an opposite opinion, we should do it gently and skilfully, so as not to irritate our neighbors.
Wow. You do not always have to say everything which is true. I take this to heart, because I love "being helpful;" saying what I know, adding to the conversation "fascinating" extras or funny bits. But it profits me nothing to always be firstest with the mostest, and probably rarely profits the other.
Also, from St. Arsenius the Great (whoever he is):
I have always something to repent of after having talked, but have never been sorry for having been silent.
There's grace in shutting up.......