However, that becomes a recipe for life, and I am more concerned with technical issues at present. All are of importance, depending upon the circumstances, and almost all three come into play together. Hitting involves moving a limb quickly to strike a vulnerable part of your opponent's anatomy. If you don't want to get hit, you can hit first. Again, conceptually this is simple, and there are many ways to do it.
Evasion involves moving away from an attack.
An attack has a trajectory that leads to a target. If you don't want to get hit, move that target away from the trajectory. There are several ways to do this. Blocking involves putting an obstacle in the way of the attack. Determine the trajectory, and put an arm or a leg on that path.