For me personally, it's certainly been an iterative process. I like to think of focus as any other habit that I want to form, so from that:

- Schedule time for it

- Understand that I will have slip ups and that's okay

- Make it hard to do the bad things (in this case, I have domain blockers to stop me redditing, I move my phone to another room etc.)

- Make it enjoyable. For me it's finding a particular energetic DJ set and just bopping along while I do the focused work.

And so on.