Sadly, a template is not going to be of much help to you. There are so many variables, including face shape, thickness or even presence of connectors, smile lines, etc, that a simple template won't work.

For a circle beard, the rule of thumb is to take your trimmer and shape it wide...leave it beyond your connectors, or your smile lines. Then, if necessary, whittle down the sides *symmetrically* until you like the look. Do it very gradually and conservatively, though...it's quick to cut down, but takes a long time to grow back.

After you're happy with the shape, live with it for a day...and refine the shape if you need to, after that. Sometimes the difference between a good beard, and a great beard, is the tiniest little tweak, sometimes nothing more than a few hairs, one way or another.