A heavier paper will give a nicer effect. Watercolor art paper which is about 90 lb. Then complete the design using your regular stylus. This does not work well with detailed stencils. It is also a good idea to have a copy of the design nearby to guide you where the details are.
Some people suggest using two stencils, one normally, and one on top as a guide.
Much as I would love to sell twice as many stencils, I have never been keen on this method and it only works if the paper easily sandwiches between the stencils which should be taped together on one side. If the design is in the middle of a larger piece of paper, this won't work. You do have to align the paper up where it had been. I shine a light on the paper to do this. Also, there is no right or wrong side to a stencil, so you simply flip it over to get a mirror image.