I make paper window templates for finding my cut area. Place the window and move it around w/ a taped mirror so I can get an idea of what will look good. But my windows aren't as perfect as my papers, so when I find my spot I usually put little marks on the papers and a tiny bit of glue to secure and free cut around them (usually from the back) if I can't see enough detail from the back I take the shade off a lamp and put it under my ironing board as a make shift light box.