Among the eighteen commitments of the mind-training practice mentioned by Kyabje Pabongka Rinpoche in "Liberation in the Palm of Your Hand", there is one about not speaking about others' defects. In fact, according to Pabongka Rinpoche, we should not think of others at all. That is, we should analyse our own faults and not look into the faults of others at all. He says that "Otherwise you will only look for faults in your fellow practitioners, the members of your monastic college, or the monks in your house at college, etc; you will then naturally find fault even in buddhas. Do not attribute faults to others, for if you do, you will ignore people, belittle them, and so on all the more". ("Liberation in the Palm of Your Hand", 2006, Day 19, p. 267).
I always try to remember these words whenever I catch myself criticising others. It is important to be mindful not to hurt others with our speech and not to judge them. Another method I use is to remember Mother Teresa's words, "If you judge people, you have no time to love them."
A famous Theravadain monk wrote in a book "How to Overcome Your Difficulties" that "there are various ways to correct a person if he is wrong. By criticising, blaming and shouting at him publicly, you cannot correct him. You must know how to correct him without humiliating him. Many people make more enemies by criticising others. If you can tell him kindly, with the intention of correcting him, he will certainly listen to you and some day he will thank you for your guidance and kindness. "
"Whenever you express your views regarding certain matters, always try to use words which would not hurt the feelings of others. There are various ways to express your views gently, politely, or even diplomatically." ...
"You should not lose your temper when your faults are pointed out. You may think that by showing your temper and shouting at others you can suppress or overcome your shortcomings. It is a false and wrong attitude to adopt."
"Cultivate tolerance for tolerance helps you to avoid hasty judgements, to sympathise with other people's troubles, to avoid capricious criticism and to realise that even the finest human being is not infallible. The weakness you find in your neighbours can be found in your own self."