Ask HN: How do you get and stay in the "zone"?

I have heard HN'ers describe being in the "zone", a mental state where you block out the entire rest of the world and are extremely productive.

I used to be able to get there regularly, but I went through a stage in my life where I had an enormous amount on my mind, and hence a lot of serious distractions. Life has since calmed down, but non-serious distractions have taken the place of the serious distractions.

I am fortunate to have blocks of hours at a time where I have nothing to attend to but my own work. What are your mental strategies for making the most use of them?

Thank you!