There are probably any number of ways to make a kiln carving pattern, but I’m fond of the way I do it, so that’s the one I use.
Determine final pattern size. I like to keep things under 6″ x 6″ (15 cm x 15 cm) for flat glass. For bottle glass, I try to keep things within 4.5″ (11.4 cm) wide because that’s how wide a regular wine bottle is when you melt it flat. The patterns can be printed at different % for larger or smaller projects.