Step 1: Making a template
I laid the wax paper over the tank and taped it down with some masking tape. First I marked out the hole for the fuel cap.
Next I placed on hand on the center of the tank and slid the other hand down the wax paper until I went passed my desired decal size or the wax paper started to bunch up.
Marking these spots allowed me a general idea of the limits for my decal. This allowed me to draw a smooth shape for the outline of the decal.