I like to use a turkey lacer to hold the stencil firmly on the cookie top, especially when there's little room to put my clunky fingers without covering up the stencil.
I use turkey lacers for popping air bubbles, marbling, and a few other things too. They're a handy tool!
Agree also with how the poll is shaping up, insofar as a thicker icing laid in a thin layer is generally better. Though icing consistency can vary (and still give good results) depending on the size and detail in the stencil.