I've only fallen once, and it was years after I switched to clipless. Just lucky, I guess.

All I can recommend is always unclip the same foot, do it as soon as you realize you are going to stop -- not as you are actually coming to a stop -- and lean the bike over to the unclipped side as you slow, so a gust of wind or a pothole is much less likely to throw you over to the still-clipped-in side, causing you to crash.