At the end of the workday, shut down your consideration of work issues until the next morning. If you need more time, then extend your workday, but once you shut down, your mind must be left free. Use a shutdown ritual (like saying a phrase or mantra at the end of the work day) to make the distinction clear.

Walks in nature will boost concentration 

If every moment of potential boredom in your life is relieved with a quick glance at your smartphone, then your brain is not ready for deep work. Schedule in advance when you'll use the Internet, and then avoid it altogether outside those times. Enforce at least a 5 min gap between the current moment and the next time you can go online, it separates the sensation of wanting to go online from the reward of actually doing so.

Identify a deep task, that's high on your priority list. Estimate how long you'd normally put aside for an obligation of this type, then give yourself a hard deadline.

"Productive meditation" (really bad name IMO) is to take a period in which you're occupied physically but not mentally, e.g. walking, jogging, driving, showering, and focus your attention on a single well-defined professional problem.

Quit social media.