The Number 1 rule in zombie combat is don't. You want to avoid the fight at all cost. LV Corby is a leading security expert who invented the concept of the panic room. He's been on CNN and on Oprah; he's been all over the place. He says that when a situation devolves to violence, there are no winners, there are only varying degrees of loss. That applies doubly in a zombie outbreak situation.
When the dead rise and try to eat the living, there's going to be no more hospitals to go to, there won't be the corner store. In a zombie plague, all resources will be quickly dwindling. That means food will be dwindling, water, medicine. Other resources are your time, your energy, your focus, your moral. If you waste time dispatching a zombie in front of you when you have the option to get away, you've only put yourself in a lesser position to survive in the next encounter that you face. You've wasted time, you've wasted energy, you've taken your focus off of greater survival. What you want to do at all cost is avoid the fight.