I use the Pomodoro technique, and it works like magic for me.
I get into deep focus mode for 30 mins and take 5 mins break after it.
I do this for at least 4 hours a day.
Surprisingly I don't get tired even if I work for 10 productive hours a day.
I like to do a cardio workout like cycling or running I find getting into a flow state or runner's high helps with focus and boosts your energy.
That sound interesting. I'd love to try it.