the simplest (or cheapest) is to grab a jar of etching cream from a hobby store, some mac-tac ..usually found in the kitchen depts or craft departments of big stores and use the mactac as a stencil ... youll have to hand cut if you dont have a plotter and either hand cut,trace image and remove the stencil parts you want etched,
Armour etch is a popular glass etching cream, follow the instructions.
if you want you can print an outline of your design or text and apply it to the stencil and cut with an exacto, I USUALLY APPLY AND RINSE TWICE..THAT WAY IF YOU MISS SPOTS THE FIRST TIME, YOULL GET THEM THE SECOND TIME (Scuse the caps)
..Plus it will give a more uniform etch.