Trackdays and books.
But not just "go out and ride around" trackdays. Usually I'll take whatever course or training is offered - everything from stepping down to the C group to go through the supervised sessions again, to hiring the video chase cam guy. Video works *really* well to show what you are and aren't doing, and how it's different than your perception.
I also don't usually just go out and try to run fast laps at the track. I focus on two or three turns with a common element (picking braking point/entry speed, exit point, bringing bike upright, whatever) and then basically cruise the course between those points, reviewing and prepping.
I do this on the street in some ways, too. You don't have to be going 10/10s to learn something. I play with traction control and ABS all the time - seeing what conditions will tr***** the electronics, then how I can be smoother and NOT tr***** them. People who have ABS and never use it befuddle me - I deliberately activate ABS under different conditions almost every time I ride, to test braking conditions and surfaces.
KeS