Eating Slowly

One technique that I am finding really useful is eating slowly. Chewing every bite more that I usually would.
I'm also trying not to 'prepare' the next fork-full of food, until I have swallowed the previous mouthful.
This forces you to look up while you are chewing rather than at your fork or at your plate. And once you do this more often, you realise how often other people look down at their plates when eating. Even when chewing a mouthful of food they are looking down at their plate preparing the next bite.
Slowing down my eating, having breaks to wipe my mouth, or sip water, makes meals last longer and gives you the sensation of feeling full without over-eating. It's hard to do at first, but it surprises you how many other people don't look up at all while they are heading. After all it's just food. Look up into the faces of the people you are sharing a meal with and enjoy the company :)