I think keeping your hands up is important. I've attended some self defense classes and this seems to be central to a lot. You don't hold them up in an aggressive boxing stance or anything, more of straight out with your palms facing the person. You are supposed to verbalize that you don't want to fight while you do this... In the event that this gesture of non violence doesn't stop the other person from attacking, at least you have a chance to block or deflect..
This "palms outward" reaction was the last way I actually dealt with the last tw*t I met starting on me in a club. He deliberately walked into me and spilled his pint, then walked right up and started staring me in the eyes with a dead look on his face.
Thing that made me laugh is he was scrawny asf, slightly shorter than me and looked like he weighed about 10 stone. If a huge guy does that, I can think "oh s***" and respect that he has that bulk to throw around, even if he's being an idiot. But I really don't understand these little men who try to act like they're really hard...there seem to be a lot of them.
The sort of losers that would lose a straight up fight very badly, but probably carry a weapon or sneak attack like the p*ssies they are.
Of course my primary concern was that he was holding a glass pint mug, a neat little force multiplier that could do me a lot of damage.
So anyway, I said "I don't want any trouble" and went palms out quite naturally without even thinking, but he just continued staring for at least another 10 seconds. Then he did a dumb little half-smile and walked off ****ily.
I used to do martial arts so had it started off, I probably would have managed to block the glass but got it stuck in my hand or arm as his first move. Potentially very nasty. But at the same time I would have quite easily physically overpowered him and f***ed him up badly afterwards. At the very least we're talking a broken leg/kneecap, as he was standing at an angle that would have made it very easy to land a heavy kick there.
The thing that just puzzles me is why these people even do it in the first place. Small brains + large glasses of alcohol? They have literally nothing to gain, particularly by starting something with someone bigger than them. I guess they assume the bouncers will break it up and they'll come out looking big...
EDIT - Interesting tip btw. A lot of the techniques I used to learn used an open hand rather than a fist. I was reading a book by an ex-SF guy talking about personal defence recently, and he says that actually he'd almost always suggest using an open palm when striking at the head.
Apparently it's not only much easier to land, but even a slight glancing blow to the jaw with an open palm will likely break it, because you hand wrenches your opponent to the side.