I really enjoyed the book: Nonviolent Communication: A Language of Life by Marshall Rosenberg - which despite the title, is actually very relevant to this topic.

I picked it up after hearing a number of very positive reviews, and despite my skepticism, I now understand why it's so highly praised.

I'd try to provide a brief summary, but I know I wouldn't do it justice. I will however say that it's almost certainly one of, if not the best, book I've ever read on improving interpersonal communication and relationships.

The author has a phd in psychology, so the advice has some real science backing it up too.