Templates

Artists use templates quite often. While to some it might look like "cheating," there is an art to properly using and positioning a template. Much of the work involved comes from knowing when to and when not to use one. Some basic rules of thumb when making these decisions are listed here.

Try not to mix template lines with sincerely rendered contour lines. The change in line quality between an honestly drawn figure and a ruled template line is more distracting than an inexact circle will ever be.
Make sure that the template is the proper shape. Just because you think you know that tire hubcaps should be round, does not make a circle the proper shape. More often than not, what you know to be a circle is actually an oval, and you are allowing your judgment to cloud your vision with silly assumptions.
Use templates of the proper size. The width of your pen or pencil will make your figure somewhat smaller than the template outline. Make sure that you allow for the width of you drawing tool when selecting a template.
Be careful of media bleed. Ink is especially notorious for seeping under stencils and leaving unwanted messes. Shy away from felt tip markers or other free flowing ink or paint tools when using templates. Often it is better to use a template with a pencil and then to ink the pencil line after the template is removed.

Using a Template as a Painting Stencil

Templates can be used as stencils, but as with all stencils, they do have a propensity for bleeding underneath. To minimize stencil bleed, use brush strokes across the edges toward the center of the stencil area only. Optionally, gentle direct downward pressure can be applied to the brush to neaten the edges.

Brush strokes away from the stencil center and across the edge of the template force unwanted paint under the edge of the cut out area.