For me the crucial idea is that we're all people together.
Some of us are more experienced people who show the newer ones how it's done. This means that we give instructions about correct behavior, but we also have to model correct behavior. We can't yell, "Be quiet!" or spank a child to teach him that hitting is wrong; it doesn't make sense.
I don't entirely agree with Alexander's advice:
Show no personal displeasure when meltdown or undesired behaviour occurs. Be utterly undisturbed.
It's true that being gentle means not freaking out over every little thing, and it's especially important to be calm and factual when correcting a behavior for the first time when the child might not know it's problematic. However, when the behavior is one that we don't do because it hurts another person's feelings or body, acting robotically serene does not get the point across and actually works against making the point. My older child is challenging in many ways, but he has very rarely attacked me physically, and I think it's because when he did, my reaction was, "OWW!! You hit me! It hurts!" with a very shocked expression, and this got him to apologize and try to make it better--much more effectively than my ignoring the pain and sending him to time out.
My goal is not to teach my children that they'd better behave to avoid being punished by someone else, but to teach them that we do the right thing because it is right.
One of the most helpful strategies to calm myself is to remember that my child is really only very small
. That resets my perspective and helps me to work with him instead of defending myself against him.
Adventures in Gentle Discipline
by Hilary Flower (best for kids under 7)
Liberated Parents, Liberated Children
and How to Talk So Kids Will Listen and Listen So Kids Will Talk
by Adele Faber and Elaine Mazlish (useful from the beginning but mostly applicable to older kids)
Parent Effectiveness Training
by Thomas Gordon