I've also wondered how you do this. If you are talking about embroidery designs made specifically for quilting, I will try adjusting the upper tension as suggested above. However, if you want to do an embroidery design and then incorporate it into a quilt top, I am definitely looking for the correct way to do this. I recently posted a baby quilt I did with embroidered designs. I doubled the background fabric (thought it would look better) and used tear away stabilizer. After the design was embroidered, I sewed the square to the quilt top and then proceeded with the batting and backing and basting. I was doing SID but felt like I needed to stitch inside by the design. FMQ would have been perfect but I am not confident doing it. I am quite sure there are better ways to go about incorporating embroidery designs into quilts and will watch this with great interest.
http://www.quiltingboard.com/picture...s-t248102.html