It would make self-protection a lot easier if you could learn the secret ninja death touch, or replicate a Vulcan's ability to touch a nerve in your shoulder to make someone pass out. Unfortunately, real violence requires much less finesse. You should put all of your strength into each strike (a fine point sometimes forgotten during slow practice). But here is one of the dirty little secrets of the martial arts world...you could do tremendous damage to your antagonist if you knew absolutely nothing about technique, but incorporated one small routine into your training regimen. A training routine that gave you..."heavy hands".
What the hell are heavy hands? And how do you get them? Heavy hands are the result of hours of hitting a sandbag. Not hard and fast, but slowly and relaxed; letting gravity take it's course and momentarily sticking to the bag. Using your fist; hammer fist; knife edge; palm; fingers; elbows; ulna bones, one-knuckle punch--and any other way you care to hit someone.
Basically, all you do is get a coin bag from the internet and fill it with play ground sand from the hardware store. Coin bags work well because they are soft and won't cut the skin on your knuckles.
Some Japanese martial arts incorporate a similar training routine with "makiwara" boards. However, these bamboo-based boards are hard and over time actually alter the shape of your knuckles--for no good reason in my view, not to mention problems with arthritis later in life.
The sandbag--if you punch it daily--will alter the shape of your knuckles slightly--but nothing compared to the makiwara board. And you can achieve heavy hands (and arms) by using the palm, hammer fist, elbows; forearms (ulna bones), and finger tips. Hitting the bag for 20-30 minutes a day, you will notice a difference after a few weeks. You hands will feel...well, actually heavy. And with heavy hands, a normal strike will greatly outmatched untrained hands/arms--guaranteed. So if you do NOTHING else in self-protection, go hit a sandbag.