I usually design something in my head, then translate it onto paper and finally either trace that or freehand onto clay. Normally, designs have to be tweaked a little - for instance, the dimensions may not work, the stone size may throw the design off or it just doesn't work!
I wanted to make another example of how to set a stone and chose a gorgeous dichroic glass cabochon that screamed "Galaxy" to me. So that was my starting point, then I designed around it. The bale was inspired by a left over piece of oval shaped clay I had and I have to say that I love how that's worked. I think I may use this design again on other pieces.