Here's the process I went through for my Sugar and Spice Pin up I recently did.
For this pin-up, I wanted to portray a Bettie Page type character with a bondage theme, but keep it a little more light-hearted. After going through a few roughs I came across the idea of having her come out of a bondage themed cake and ended up with the rough below.
So as you can see, the final didn't change all that much from the rough. The main critique I received was about the cake. A friend pointed out that the layers should be switched so that there is more of a visual rest between the model's stocking and the ones on the cake. They also recommended adding a shibari pattern to break up the layer with the ball gag and straps.
For the final line work, I switched the cake layers, redesigned the ball gag layer with the shibari design, added a bow to the stocking layer to break up the lines, shifted the model's pose slightly to center her a little more, and added some detail to the model's outfit.
Finally, I scanned the pencils, printed them out in blue line and inked the piece. There weren't too many changes from the final pencils besides leaving out some of the details that would look better being added digitally. Once the inks were done, I scanned them in, cleaned up the lines in Photoshop and colored it.