Decide which area of the jar you want to paint. A small hint from our side: The less curvy the jar, the easier it is to decorate.
Before getting started on your glass, you should design the lettering on a piece of paper. Sketch a rectangle in the size of your desired letter design on paper and mark the middle for orientation. Add additional supporting lines for each row that you want to write in. This helps your letters to be equal in size and the words to be on the same level.
In case of a typo wipe the ink off the jar and restart. The ink will be dry and wipe-proof after 24 hours, which allows you plenty of time for alterations.