Foundation of Self Defense

1.  Awareness. This is huge. Just by this alone, you will be able to avoid most of dangerous situation. Awareness is the critical key that will determine you on preserving life or not. It covers beyond just hand to hand combat, it also covers prevention, the difference between winning and losing or even life and death.  For example, checking your locks at home, your electricity switch and other crucial things in your house can be the best way to prevent potential robberies or your house burned down due to negligence.
2. Hand to hand combat or empty hand fighting. Ability to fight empty handed really boost self-confidence   for real. When you are training the right way, you cannot BS yourself about what you are good at, what you are bad at and what you are afraid of. Having proficiency in this area will really help you in most of combat situation that you might face.
3. Weaponry training. Most real street fights will probably use some weapons like knife, stick and gun. I think its important to know how to use weapons before knowing how to defend against them. Also, using weapon is maybe the only equalizer you have against multiple opponents.
4. Multiple opponents. I think facing multiple opponents is difficult, but one needs to prepare for this. To achieve that, getting good at fighting one opponent is a must. If you suck at fighting one opponent, imagine fighting multiple of them, forget it.  So besides investing time to be excellent in empty hand fighting, one needs to learn the strategies in facing multiple opponents.

Those four is what I think the foundation of self defense. When you cover all four well, i am confident that you have massively reduced your chance of becoming a victim.