A Simple How-To Rated 4 out of 5 stars
It took me a while to figure out how to use this. For the benefit of others, and myself a year from now, if I've forgotten:
To create a template: open your favorite text editor and make a simple html file (example below) containing some CSS style rules, html tags and/or content. Save it to the folder of your choice. (I chose a folder in my dropbox, to make my template available on my desktop and my laptop.) Choose this folder as your default path in Stationery Options -> Default folder.
To use your template: when composing a message, right-click somewhere in the body of the message (with the Edit tab active), and choose Change Stationery. The first time, you will have to choose the "Other Stationery" folder, but after that the template will be listed as one of the choices. Alternatively, you can hit the drop-down arrow next to Write or Reply and choose a template or "Without Stationery."
The next time you compose a message, whatever template you used in your previous message will be in effect, but you can switch as described above.
Note that you can edit the template while in your message draft, by going to the Source (HTML) tab.
Now for a sample template, intended as a starting point. You may put internal style rules inside the head, but they won't show up in gmail; therefore I used inline styles.
Outline template that will work in gmail
<ol style="margin: 0 0 10px 12px; padding: 5px 0 0 10px;">
<li style="margin: 0; padding: 4px 0;">item one</li>
<li style="margin: 0; padding: 4px 0;">item two</li>
<ol style="margin: 0 0 0 15px; padding: 4px 0; list-style-type: lower-alpha;">
<li style="margin: 0; padding: 0 0 4px 0;">sub one</li>
<li style="margin: 0; padding: 0 0 4px 0;">sub two</li>
<li style="margin: 0; padding: 4px 0px;">item three</li>