This tip is one that's been around for a while . . . so long, in fact, that it's well-ingrained in both my Sprouts. At each meal, I have them start with the salad or veggies, move on to the "main dish" (soup, sandwich, pasta, etc.) and save any "treat" like bread or crackers for last. On more than one occasion, when eating out, they've actually informed our server that they need their salad before they can eat anything else.
Not only does it give them a great incentive to finish their greens, but if they happen to fill up before they've finished, at least the most nutritious food got in first!