Summarize this article:

Consider what the stencil is to be used for--say, a small decoration on a box or a pattern for use on your walls. How will your use of the stencil influence the design you can use?  Here are a few specific points to consider:  Don't use paper. Determine what size of stencil you need. If the stencil is going to be large, it is okay to include small details. If the stencil is going to be small, a simpler design should be used. Know how many colors you want to include in the stenciled image. You can use multiple stencils and each will be used with its own layer of color. These factors will affect the amount of materials you need and the number of stencils you need to create. There are a variety of materials that are suitable as stencils, but you need to consider how much use the stencil will have (one time or many?) and the ease with which you can work with the material.  Cardboard or foam board are good for large, simple stencils on flat surfaces. Paper works for a single-use stencil on either flat or rounded surfaces. Poster board holds up better than paper and can be used on flat or slightly rounded surfaces. Plastic or clear acetate are good if creating reusable stencils for either flat or rounded surfaces. Frisket film, which is a clear film with a slightly sticky backing, is good for flat and rounded surfaces.

Summary:
Think about your overall design plans. Choose the type of stencil material you want to use.