Manners really are all about behaving appropriately for the situation you are in.
How you behave in the forest for example, is different to how you behave in the city.
How you behave when painting is different to how you behave when riding in a vehicle.
For example explain that it is innappropriate to run around in a shop, or a museum, or during a performance etc.
That it is innapropriate to shout in a library where others are concentrating on reading.
That for the wild plants to thrive it is innapropriate to pick the wild flowers. If we all did it then there would not be many left.
Explain that it is OK to get dirty when you are wearing your "working/play" clothes but not OK to deliberately get dirty when you are dressed for a special occassion like a wedding etc!
That it is OK to mess up your hands when making pastry etc but not OK when using ink!
I am sure you can think of many other occasions when you might have to explain!
This would be the way YOU would like to be treated in all situations.
Things like: sharing; being kind; taking turns; listening ..ie letting the person who is talking finish before you have you have your turn; being helpful; saying please, thank you, sorry, etc