Find some kind of lessons,something that involves a good bit of contact. Problem with books and videos is that you don't get used to having someone whale on you. Practising with friends you get into a routine and don't try to really, really hurt each other and a big part of surviving a fight, when you actually have no other choice, is how you react after, say having your nose or ribs broken. Some people curl up, some people explode with aggression, you might think you'd know what you'd do, but I've seen "trained" people just stand there, dazed, not really aware of what just happened to them, trying to recall some routine they learned... I would try boxing first because you'll have to deal with someone trying to actually beat you unconsious and that will sharpen your reflexes and teach you distancing rather quickly. Even in some of the X against 1 classroom situations mentioned, there is still a level of withholding and safety, because you don't actually want any students killed, so people tend to back off and you can end up with a dangerously false sense of your abilities...