This is part habit part instinct.

Dogs, no matter what size they are, have the instincts of wild dogs.

A dog that is fed regularly is open to the temptation of the wild dog - save some for later! Don't let anyone else that wants to eat the same stuff as I want to eat know where my food is!

Find a place to feed your dog where it can be isolated with the food for five minutes - the bathroom is a good place.

Put the food down, shut the door and after exactly five minutes go and pick up the feed bowl, put it out of reach and ignore your dog until it is lying quietly. DO NOT GIVE THE FOOD BACK TO THE DOG!

At the next feed time do exactly the same thing. Be strict!

Also cut the food you give the dog to half at each feeding time to encourage the dog to eat it all.

The dog will soon concentrate on eating.