My family, on my father's side, comes from the "Vilne Guverne", that part of today's Belarus that often changed hands from Poland to Russia to Lithuania. My Great Grandfather was a "shtepler" (leather craftsman) in Radun, the hometown of Rabbi Israel Meir HaCohen Kagan, best known by his appelative of "Chofetz Chayim".
One of the issues the Chofetz Chayim was most concerned about is the idea of Lashon HaRah or "evil tong", generally translated as "gossiping". Even when the translation is not 100 percent accurate, it is close enough for government work. The idea of Lashon HaRah is that when you speak about others you not only tarnish them but also yourself. So if we cannot talk about others...what do we talk about?
It is not that we cannot talk about others at all, but that we need to be careful about it and talk only about facts and not let our personal feelings color the conversation. It is very different to say that somebody is not living up to the demands of his/her job than saying that the person is lazy. In the first case, we base our comment on facts, in the second we are giving a personal opinion that will already influence the listener in his/her perception of the person in question. The first case is legitimate commentary, the second is Lashon HaRah.
The use of unproven facts or assumed facts used to tarnish somebody else is also Lashon HaRah even if they are facts... Saying "You should not trust that person because he/she did such and such" is definitely Lashon HaRah.
Most of the time we do not realize the implications and consequences of what we say and that is where the problem is. Khalil Gibran, the Egyptian poet, said in one of his books of proverbs that "when the words leave your mouth, they are not your words anymore" and that is probably the best description of the consequences of Lashon HaRah.
It requires discipline to avoid the temptation of talking about others in an inappropriate manner, but if it didn't require it, we wouldn't need ethical codes of behavior. Words can hurt and be more damaging than a blow in the face, yet we are a lot less careful about words and we dole them out way too freely.
In Argentina there is a popular saying which originated in one of the TV programs a long time ago and became sort of shorthand: "Put you brain to work before your tong begins to move". This saying also points to the problem of Lashon HaRah. If we really think about what we are about to say, chances are that we will avoid saying what is inappropriate - but more often than not, our words just come out bursting without self-censorship because we want to keep the conversation going and fill in the silences...because silence can be frightening.
But silence can also be a source of strenght, and we often forget that. Probably a good advice would be "If you have nothing to say...don't say it!"
We just finished Yom Kippur, and Yom Kippur stresses the need to ask forgiveness from those we hurt by deed or by word - because the word can also be a weapon, and one very powerful indeed. Political campaigns are full of smearing bouts of Lashon HaRah designed to tarnish the other candidate. Our tradition considers it wrong, and there is no two ways about it.
But Yom Kippur provides us with another opportunity - that of being able to move beyond our mistakes and change our behavior, because without changing our wrong behavior, repentance is not truly complete.