There used to be a tutorial on Quilt Writing that was on a Pfaff website called "Behind the Seams". It's not there now, but basically, you just free motion write on your quilt. I searched a few places to see if I could find the tutorial elsewhere but no luck.
I did practice quilt writing and did a bit of writing on a Princess and the Pea quilt for my youngest granddaughter. Have a look here. If you practice on scraps first, that becomes a very good option for you.
One of the main tricks is to figure out how big you want the writing. The tutorial had you print it out the words you want on your quilt, from your computer on paper. Cut the strip of words out for the area that you are working on, tape it just above or just below where you intend to quilt write. Then you have that as a guide for spacing.
Have a look. I practiced two times, before doing it on the actual quilt. I was pleased with the results. In fact, when I do a kids quilt, I always try to quilt write in it, even if to add the name.
http://quilt-knit-run-sew.blogspot.c...s-and-pea.html