Ways to improve concentration and increase attention span?

Are there any tried/tested ways that are known to succesfully imrove concentration and increase the amount of time you can keep your attention on one thing?

I’m sorry. What?

I know there’s some sort of occupational therapy for ADHD people, but as my medication as always been good enough for me, I haven’t done it myself. People say it works, though- and I’m sure that at least some of the techniques are transferrable to non-ADHD folks who just want to be able to concentrate better.

Uninterrupted sleep works wonders.