You've never used flats then? Not even as a beginner? How unusual.I never understand how you can even start off with flat pedals, how do you pull it up for the first move off? I get into a right pickle when I hire flat pedal bikes on holiday ...
I do it without really thinking about HOW I do it, but I have a feeling it might be something to do with sticking the top of your foot under the pedal and lifting it up to the required position; or spinning it backwards, or a bit of both. I just know it's not difficult.