Whenever you notice a fault in another person, check where you have that fault yourself. We have a strong tendency to notice our own faults in others. This awareness gives us many opportunities to learn about our own shortcomings -since it is easier to recognize a fault in someone else than in ourselves."
What fault do you commonly notice in other people? In what ways do you have that fault yourself?
Use this awareness as a tool to stop yourself from speaking against others. Who would want to speak against others knowing that you are merely drawing attention to that same fault in yourself?!
Today, catch yourself in the act of criticizing others. Then think about the implications for yourself.
(see Talmud Kiddushin 70b; Rabbi Chaim of Volozhin - Ruach Chaim 2:1)