Maybe look for a venue with fewer distractions? For me, a workspace that has only the relevant work materials and sufficient space to work is a great way to get into flow.

My personal failing is not getting to nearly all the reading that I want to accomplish. The best thing I have found to get through a lot of reading is a coast-to-coast flight with only a Kindle in my carry-on.

If you find yourself wandering, look at the hourglass and see if it still has sand in the upper chamber. If so, go back to work, if not, you were focused enough on your work for enough time not to notice the time running out.

There are some boring, tedious work like writing documentation and tests, where the Pomodoro Technique works well. But not for truly deep work.