To elaborate a bit more, I try to stick with the No S Diet (http://nosdiet.com/), especially the part about "no snacks". I used to be extremely prone to snacking, and it would almost always be snacks of a very unhealthy variety.

So I cut out snacks almost completely, but I still let myself eat a burger+fries or a pizza once in a while. But they count as a full meal plus a bit ekstra, so my next meal will have to be smaller to compensate. Seems to be working out.

But the biggest difference for me was changing my sedentary lifestyle. Standing as my desk, always taking the stairs, riding a bike everyday. It adds up.