For those who feel artistically challenged when it comes to drawing, using a rotary tool to create a design can be intimidating, but with a stencil anyone can create fantastic works of art in minutes.
Etching cream and stencils can be purchased at most fine craft stores and it is relatively inexpensive. Some states do not allow it to be sold in stores because of concerns of vandals using it for nefarious purposes; in those cases we have the internet and notably Amazon.com to supply these kits.
Also of note with etching cream you should avoid trying to use it for large areas due to its sometimes inconsistent nature. For smaller jobs like small mirrors, wine glasses, etc., the cream works fine.
To use one of these kits select a vinyl adhesive-backed stencil of your choice (or you can get a plain adhesive-backed vinyl sheet to cut your own design). Apply the stencil to your glass piece, smoothing out any air bubbles with the included brush, and apply a liberal amount of cream to the stenciled area. Wait a few minutes for it to do its work and once the required amount of time has passed wash off the remaining cream in warm water, remove your stencil and you're done. Beautiful etched glass remains.