Go for vulnerable areas, eyes, nose, throat, balls, knees.
Sure karate and that stuff is nice, but if you are simply trying to get away from someone, one pop to the nose is all you really need. It hurts like crap and makes your eyes water, making it hard to see.
Nobody is invincible, even unarmed and 1 on 1. In reality, if you train a full contact art, it would give you a big leg up on any single other person, but if 5 guys jump you someone pulls a gun, guess what, you're in trouble.
Be cheap, efficient, and precise. Don't "brawl" at them.
Attack their weak spots with your strongest force. Especially if this is self defense. Balls, eyes, ears, solar plexus, nose, chin, neck, all vital areas that you can attack. However, never do so for play fighting. I will repeat, only attack such areas in self defense. The are very vulnerable and if attacked with enough force quickly, can guarantee incapacitation in a small amount of time.
google it! if you're looking for some MGS style combat, you may wanna have a look at krav maga
any type of cqc is based on weight and gravity. its being able to be fluid, change your center of balance, while upsetting the other persons. lol. the only way to really practice this is to join a martial art =P