Have apples handy.
As you pass the stack of brownies, calculate in your head how many hours that will cost you in the gym before you indulge
If you eat and are still hungry go for a walk. Then if you are still hungry top up, but may times you won't need to
Skip the cheese
Look at how skinnier people around you eat. If out for dinner, do they order a regular coffee while you order the one with whipped cream?
My wife's favourite saying - just back away from the buffet.
(Small plates help if you've been trained to eat everything on your plate)