Top 2 in Top 10 leading rules in Western high-end cuisine.
Your napkin should be opened and placed on your knees. Never get your napkin in front of your shirt or skirt. Anciently This is normal, nowadays it is the height of vulgar. If, for some urgent reason, you have to leave the table before the end, you should put your napkins on your couch. This tells the server that you intended to return.
When you're ready to sit down again, just replace the napkin on your knees. If your napkins fall to the floor, you can accept it unless the House has a butler or maid near the table. In those cases, they will remove the napkin and replace it with a new one. Never put anything in your napkins (especially not food).
Once you're done eating, make a neat napkin on the left side of your plate.