I work 7 days/week round the clock with short power naps - I been doing this since my university years ('79).
Couple things that make a positive difference:
Nutrition - make sure you are nourishing your body with either good food and/or vitamin supplements. If you work long hours or under duress, B complex vitamins are very helpful. Don't take vitamins on an empty stomach.
Exercise - even simple regular walks will boost you energy levels.
Rest - Sleep when you are tired. Do not try to sleep when you are not tired. If you can't sleep, go do something.
Breath! - Oxygen is what fuels our brains and learning to breath properly can make a huge difference to your overall sense of well-being. Don't crap up your lungs with smoke.
4 hours of deep sleep can totally recharge your system.
Unfortunately, our 9-5 M-F grinds totally conflict with our natural cycles - one of the reasons I have broken away from that loop and work according to my own needs/cycles.
-Dino