You'll actually find the directions for doing this in a couple of places. First in your SFD Pants Kit instruction book, it's on page 15 #11.b. The second location is in the new SFD Leggings Leaflet. Just click on this link. You'll have fun making leggings that finally fit you properly.
In addition to this, my friend Joy, from Joyful Expressions, has recently made a video with her sewing buddy, Phylly, showing how to draw these princess seam line pants using their SFD Pants Pattern. Have fun watching these two lovely ladies as they show you this process.
The only comments I would make are - when they show you the back dart and how it relates to the pants back leg seam, the dart should have been moved over to be directly on top of the seam. Doing this means that the gentle curve of the seam going into the dart would have the same curved shape on either side and will make sewing it much easier and it will lay flatter on your body. I actually show how to do this in the Leggings Leaflet.
The other comment is that drawing the curved extension of the seam can also be accomplished using the SFD Designing Stylus.
Enjoy this tutorial - it's fun and easy to watch.
Thanks ladies...you did a great job. I'm so glad you're enjoying and benefiting from fitting and sewing with Sure-Fit Designs™.
In addition to Joy's video, there is also a Sure-Fit Designs™ video that is directly related to this topic, that being the flat backside. Perhaps you may be interested in watching this one as well if you happen to have this flat backside fitting concern.