John August, asked by a working screenwriter how he can keep improving throughout his career:

My advice for you is to dedicate one day a week to disassembling good movies. Take existing films (and one-hour dramas) and break them down to cards. Think of yourself as an ordinary mechanic given the task of reverse-engineering a spaceship. Figure out what the pieces do, and why they were put together in that way.

I think this true for any craft.

[It’s a great way to hone one’s touch and grow new skills. I especially like doing it as a group exercise to learn what others see in something that I don’t.]
Source: Daring Fireball