Lighting Your Model Consistently

If you are working from a live model over several sessions, and have to move your lights around between those sessions, it can be time consuming making sure your lights are in the same location, and at the same height each time.  You'd have to keep moving the model and light, and compare it to your painting from the session before.

A trick I learned from Marvin Mattelson was to place a small object on the modeling stand after your model's first pose, and trace the footprint of the object, and the shadow it casts.  (he used a small aerosol can he had in his materials locker).  Rather than trying to compare the complex shadow shapes on your model, you just have to compare the tracing to the shadow cast by the light when you set up for each day of painting.

Once the light is in place, you only have to make sure the model is looking the correct way (at the same height, with the same expression, etc..)