First, of course, I drew my design onto paper. I traced the bodice pattern shapes and then drew in the design. My swirly pattern is based on the leaf design that I drew all over every notebook from junior high through college (miles were drawn during my one-on-one Russian history class alone), and then rather heavily influenced by Cersei's pink dress. In other words, my vines and the round shape of her swirls. Each little swirl is going to end in a two petaled beetle wing flower.
I then traced the design onto muslin with a Sharpie.
The next step was to pin the patterns into place. Try to avoid your design area as much as possible. I ended up having to move the red pin on the lower right.
Continue around the dress, matching lines as you go. I found the arm of the couch very helpful in doing this. The curve of it made it easy to lay the dress flat.
While I've previously used a window as a light box, that obviously wasn't going to work here. Just like pinning it, tracing it required curves. So, I took a round Pyrex dish and my cellphone--instant light box!
Everything shines through very nicely!
And the traced design! I used a regular pencil. My usual mechanical pencil was too sharp for the washed taffeta. Now, to bead the lines, sew running stitches near them, swirls behind them, beetle wings to the ends of the swirls, beads for stamens between the beetle wings...