Rising trot came naturally to me, in my first lesson it felt right so that's what I did.
Learning which diagonal didn't happen for a few years; I got with a trainer who had me on the lunge line and told me to watch the shoulders. Outside leg forward, up. Then she would have me yell out now, now, now, now... with the outside shoulder. Then she made me post with my eyes closed to get the feel for it. I still sometimes have to look to make sure it's right.
Learning to sit at the trot was an entirely different matter, so hard. It took me years and the use of the 'unisit' system (which is actually just a torture device for idiots like me who can't sit the trot)