Don't you worry...I'm here to aid you in this decision.
I prefer to set the napkin in the center of the plate, with a nice napkin ring. Many people like to place the napkin in the water goblet, but after breaking a friend's Tiffany crystal stemware trying to remove it, I now try to spare guests of mine - and my fine crystal - the same fate.
After you remove your napkin from the ring, place the napkin on your lap and the ring to the left of your plate. After you have finished your meal and get up to leave the table, you can place the napkin to the left of your plate, or once your plate has been removed, you can place it where your plate had been, but not back in the napkin ring. However, it's proper etiquette to leave your napkin on your lap until you get up from the table...even if you're finished eating. If everyone stays at the table and chats after the meal, it is considered rude to have your dirty napkin in sight.
Don't have napkin rings on hand? Here's how to fold one like a pro:
Fold the napkin into a triangle. Fold in the two bottom corners one quarter of the way. Fold both of the corners over one another so they meet in the middle. Fold the top point down and flip the napkin over, and you have a chic envelop shape. You can leave it as is, or insert your silverware, a pretty flower, or chopsticks if you're serving an Asian menu.
Did these tips make it simple for you? Let me know if you have any questions. I also have LOTS of other napkin folds I will be thrilled to share with you. This was my hobby growing up whenever my mother entertained. It's fun table origami to me.