After falling into a lane of the freeway, here's what I did: I went to a deserted road, and started and stopped perhaps 200 times in a row. I practiced with the left and with the right. I practiced unclipping when at all different positions. I haven't fallen since.

Also, the advice about turning the wheel seems silly (if I can remember to do that, I can remember to unclip the correct foot), but it was helpful to me.