I don't have any rules about trying stuff, or eating what's on your plate. Our rules focus on manners and cleanliness, and respect for others:
1. use utensils (once you arrive at an appropriate age)
2. don't interrupt-- conversation means one person talks at a time, and you say excuse me if you must interrupt
3. you may eat or not eat, whatever you please from what's on offer, but you may not whine or complain or use phrases like yuck to describe the food
4. you can get down when you're done, but you can't come back a whole bunch of times (except for going to the bathroom-- DD2 has a chronic need to have BMs ten minutes into her dinner....
) when you get down, you go out of the room and find something else to do-- you can't hang around annoying people
5. use please and thank you and the other niceties of reasonable politeness
6. if you drop something, pick it up; use a napkin; try hard not to spill, and help clean up if you do spill
7. if you don't like the food, that's fine; there are vegetables and fruit and yogurt in the kitchen, and you can go get them if you want, provided you follow rule #3
8. No reading at dinner. I tolerate breakfast and lunch reading, because I'm just as guilty.
9. If you don't like something, push it to the edge of your plate; don't leave it on the tablecloth
10. Keep your hands and feet to yourself and don't be excessively silly.
and we just added a new one: you may not eat directly out of serving dishes, or handle the food in serving dishes with your hands-- no picking through for just the parts you like-- serve it to your plate, and THEN eat it.