You just do!
Us humans are not ideally suited to working random shifts, and a 2 early, 2 late, 2 night shift roster is less than ideal. When you first get posted after the college it will take some little while to adjust, and the continuously changing sleeping pattern can be a right pain.
But after a while you accept it and your body copes pretty well. I'm a bit of a night owl, consequently I still don't appreciate the alarm's presence at 5am, but the job is fantastic with never a dull day. There are those who love the morning shifts, people like me who find the prospect of a 2pm start much more agreeable, and those who have an obsession with night shifts. We all manage though, and it's worth it!
You get plently of leave too so there are frequent periods for your body to recover, not to mention regular breaks whilst at work.
On a day-to-day basis you learn what works best for your body. How you can best prepare for a night shift, when to sleep during the day, etc. For the regular early and late shifts it's more a case of having the discipline to say no to that pint down the pub and get your head down at the time you need. There is nothing funny about trying to control when you are over-tired (like the Vauxhall ad...), it'll scare the bejesus out of you and it'll only happen once!
My only other tip would be to have an appropriate bedroom, one that you can make completely dark even during the sunniest day.
Hope that helps, either way, a small sacrifice!