When I talk about others, particularly in negative ways, I am usually trying to build myself up in comparison. This doesn't mean I cannot or should not ever speak of another, sometimes it is inevitable, or worthwhile. Vipassana teacher Joseph Goldstein is reported to ask his student to not say anything, ever, about a person who is not present in the room as a way to foster right speech. Sai Baba suggests that we consider, before giving advice, criticism or feedback, the following. What we say matters, but so does why we say it, where we say it, and how.
Public correction can humiliate, embarrass, and create feelings of failure.
Check your motives before speaking. Listen at least twice as much as you speak. When we recite the Sutras or a mantra, we are engaging in Right Speech. Finally, remember that silence can be Right Speech as well, and as such is the foundation of many monastic activities and lay retreats. For more information on this step, you might wish to review the True Buddha School Net article on the topic, or the Abhaya Sutta .