Switch to pencil, the drawings appear slightly different. I chose my favorite position of the ballerina, roughly traced that moment when she posed and then filled it with my imagination.
The feet ! They got my attention, specially when the dancers danced on their tip toes.
I enjoyed using quick line drawings (3s) to catch movements of dancers, one by one and put them together to create a sequence, like they were floating all over the place on the paper.