1. Wait until the host starts to eat before eating yourself. Also, when dessert is served, wait to start eating your own dessert until the server has been seated and can begin eating.
2. Chew with your mouth closed, and don't talk with food in your mouth. This seems obvious, but it took practice for my children to master it.
3. Take small bites, and eat slowly. Young children eat fast when they are hungry and this habit can be off-putting when they get older. So teach them to slow down.
4. Don't leave the table until everyone has finished their food. Young children want to get down and run around after they are done, but this can make it stressful for people still eating. You can help them stay at the table by providing funny papers, or puzzles for them to do while they wait. Also try to include them in dinner conversation.
5. Teach them to put a napkin in their lap, and to use it often. They also need to know how to pass food and ask for it to be passed. Make sure they are not reaching across people to grab things.
We used to have manner dinners where we would try to practice good manners. We would light candles and blow them out when anyone broke a manner rule. The goal was to keep the candles lit as long as possible.