I'm very much looking forward to attending a full day workshop on NVC next week. I attended a shorter workshop earlier this year and was very taken with the philosophy behind NVC. In brief, it holds that our culture promotes the use of violent language of blame which affects our ability to communicate in a useful way and can contribute to or even cause conflict.
The idea is that to communicate more effectively we could change how we express ourselves and e.g. instead of saying "You're so messy, you make me so angry" we could say "When I saw the messy room I felt angry because I want the house to look neat and clean." which, apparently, will evoke a less defensive and conflictual response. An important part of the learning here is that nobody else is actually responsible for how we feel, that isto down to us. By owning our feelings and not blaming other people for them we can engage in a dialogue which does not provoke conflict by triggering defence in the other.
It is quite tricky, in reality...
and... of course, there is a lot more to it than that.
The Center for Nonviolent Communication