What a great idea
First on the list should be words to the effect that if they wish to have the best possible chance of surviving should anything go wrong - however unlikely that may be, then watching the Safety Briefing is ESSENTIAL!
Like others who have posted, I too am amazed at the basic lack of manners "Please" and "Thank you" costs nothing and is far more likely to get you any help you may require. PLEASE put all your rubbish in a bag not strewn all over the floor, and leave it where it can be easily removed when you leave the aircraft. The same applies to your blanket and pillow if on a longhaul flight, leave them - folded if possible, on your seat.