He really forced me to grow as a player. I've always been a very offensive player (cammy/ninjas, etc). My friends always tell me I press too many buttons, I need to AA better, and to be more patient.
One thing I would do, when I had a pretty comfortable life lead, is just hold d/b and try to react to what my opponent was doing. Akuma's AA game is super strong, so I got a lot better at that, and since his life is garbage, I learned really quick where to press buttons and to push the offensive.
I would say the most important thing is learning Akuma's oki setups. There are a few guides I watched, but they're mostly the same thing:
https://www.youtube.com/watch?v=JpK9baEUTrY
Almost every knockdown Akuma has leads into a meaty situation. Like, never finish a combo midscreen with an upper, since you give up pressure for that. I like to do either lk tatsu, hk tatsu, or vskill kick into demon flip palm. B+hp is the godlike AA normal, and leads into similar oki situations.
But mostly it taught me to be really, really patient. I haven't played anybody but akuma since December, so one thing I want to do is go back and see how my new mindset affects how I play other characters.