On the same site as above are helpful tips.
https://www.emblibrary.com/EL/ELProj...ulHow-Tos.aspx
This one has more information.
http://www.nancyzieman.com/blog/sewi...roider-towels/
I just use a ruler and mark cross hairs for the center point of design. If you have software the cross hairs can be printed on the design template.
For hooping, I mark the cross points right onto stabilizer. Match the center points of stabilizer and item you are stitching the design on.
This is the method I use for matching the stabilizer with item (towel, or fabric block, etc). Much easier than re-typing and explaining it. Scroll down about half-way.
http://www.secretsof.com/embroideryblog/
I hope that helps. Post back here if you need more help.