For my sisters shower (seen here) I bought some fabric that I really liked that when with the yellow and grey bumble bee theme and used it in several places (honey favor tops, table runner, gift wrap, and to make cute custom napkins. But I wanted them to have nice professional looking edges and corners.
Fold the edges in 1/4 inch and iron all the way around then fold 1/4 inch the second time and iron (this will hide the rough edges)
Unfold the second ironed hem
Fold the corner back(in half) right-side-facing. The picture above is a little off, but you should sew a 45 degree angle from the ironed seam created by the second fold to the corner.
I missed the ironed seam a little as you can see here, but don't worry it still works.
Turn corner right side out and iron flat again on the originally created second seam.
Sew along the edge where the fold and the napkin meet all the way around the napkin.
Fold and press as desired or make cute napkin animals with them.
I also found some help using this tutorial although I didn't like the method of dotting the fabric to sew the corners. I found it much easier for me to fold the corner (as shown above) and then sew a 45degree angle from the second seam line to the edge (you can use a sewing ruler and draw lines or use their method but I tried it and maybe it was because my ironed hems were not exactly the dimentions they had.