I have a couple tricks.
1) Eat foods high in protein. Protein will make your body feel full longer. If you make a larger portion of your meal protein, you won't crave as much later in the day.
2) Have a healthy snack food on hand. I keep a bag of almonds in my desk or apples in my fridge at home. That way if I'm craving something, I snack on those healthy foods to dillute the craving and am much healthier because of it.
Honestly it's just getting in the routine of those two things. After a while the cravings for 'junk food' subside. Once you change your diet then your body doesn't really care to have a big greasy burger any more, or if so, no cheese & mayo. It will start to crave healthier items as they'll start to taste better and 'junk' food starts to taste worse. It's initially going to be a mental challenge, but I follow the two rules above and it's worked tremendously.
Edit: Drinking extra water helps a bit but wasn't enough for me. Was still craving food after, which is when the almonds come in handy.
'91 M42 E30 - All sorts of goodies.