Oh man, this guy's so wrinkled. If you're going for realism, do yourself a favor and grab some photo reference from the internet, or just pop in the DVD and pause it on a good shot. Much of the face will be covered in shadow, so focus on the wrinkled brow, cheeks, nose and mouth. Sidious basically looks like an old woman -- no offense to Grandma ;) On the neck, draw some broken V-lines to show the skin pulling downward. Ew!