“Don't talk unless you can improve the silence.”
“Don’t say anything unless you can improve on the silence.”
“Not every change is an improvement but every improvement is a change; you can't do anything BETTER unless you can manage to do it DIFFERENTLY, you've got to let yourself do better than other people!”
“Never give advice unless you have walked the walk, because anybody can talk the talk.”
“You don't know if you can do it unless you try! :)”
“Speak only if it improves upon the silence.”