Dreaming. I couldn't tell you whether I dream in colour or not, probably the most vague of images at best, but most likely purely narrative (I'm fairly confident that if they cracked my head open, they'd find something wrong with the visual part of my brain). I might remember half a dozen dreams a year, but since I was reading about it today, I might remember one tonight, that is how it's supposed to work. People remember dreams because they're interested enough, and want to.
As for lucid dreaming, I have realized that I was dreaming in a dream before, but then I forgot about it right away. It would be cool to be able to lucid dream though, but I'm of the opinion that nothing can be taught, only learned, and people learn things because they're interested, look for the information, correlate, interpret, and incorporate information into their learning process, and become skilled at things in this way. So that if someone is a good lucid dreamer, They began with a talent for it, I think, and what worked for someone else may not work for you, and vice versa.
I didn't mean to limit the idea to physical disciplines, line a gym, I just thought I'd mention those for their physical components. I imagine that learning a new language, solving math problems, or whatever it is that you're doing and interested in would be the same.