We have a "good eaters club" which was really created for my picky eater dcb. They get a sticker if they eat well. I also sing a song if they try something new or eat something they don't like. The kids all sing it with me so there is lot's of encouragement. I praise my good eaters tons and this spurs on those that struggle.
They also don't get desert if they don't eat. They eat only what they are served.