A principle drawn from law enforcement and military survival research: the people who live through violent encounters almost always decided in advance that they would act.
Pre-commit to act so hesitation does not decide the outcome for you.
Violence collapses time. In the first three seconds of an attack, there is no room for a moral debate; whatever you decided long before is what you will do.
Sit with the hard questions now, in the quiet. What will you do if someone grabs your child? Steps between you and your spouse? Puts hands on you? Answer honestly, and answer today.
The decision itself is the technique. Rehearse it until it becomes reflex, so when the moment comes your body moves while your mind is still catching up.