Eat a healthy three meals a day, drink a lot of orange juice and water, get sleep at night. If that doesn't work, look into vitamins or medications or some shit.
I used to work 12 hour shifts and a lot of times I would go out drinking (heavily), only get an hour of sleep (If I was lucky), then go to work all day. Energy drinks helped a lot on those days, but I guess it depends on your age and the type of work you do