I guess how you make a template depends in part on the software you use.
I use Photoshop CS4 now, but have used CS2 for years.
From a sketch or an idea I have, I use the selection tool to make the rough shapes and then use a different color to fill each one -- oh, and I put each different element on a separate layer. Then I can move things around, shift the layers up or down and change things out.
I did a search and found a few posts on how to use a template, but some of the ideas might help you out
http://www.godigitalscrapbooking.com...reate+template
http://www.godigitalscrapbooking.com...reate+template
http://www.godigitalscrapbooking.com...ead.php?t=1121
One is for photoshop/elements, one is for scrapbook max, and the last is for PSP
Good Luck
I am sure others have some ideas on how they make their own templates too