I use acrylic cover button templates that I bought from http://www.thesewphisticatedstitcher.com/cobute.html
. I can't say enough about how much time and frustration it has saved me when doing monogrammed cover buttons. After I get my monogrammed circle of fabric or ribbon cut out, I turn it over and use the inner circle of the acrylic template and trace a circle around the design to where the design is centered. Then, I cut out the excess stabilizer from around the inner circle and now you have exactly where your button goes. You can do this if you don't have a template, too. The instructions here: http://girlythingsbows.com/monogrammed_button_covers.html
use the button the make the inner cirlce, but it's all the same idea, except you're using the button as a guide instead of the acrylic template: I put a small piece of double sided tape to keep everything centered while I attach the button. The Girly Things Bows tutorial is a great tutorial. I hope all of my jibberish makes a little sense.