I usually experiment with posture and physical attributes that may inform the character. Next, my impression gets a nice injection of inspiration when the costumes arrive and I can see his silhouette in the mirror. Then I go memorize all the lines and try and connect each line to a thought I think he might have. Then I show up on the day, wait my turn, and when the director calls "action," I trust that I have done enough work on my impression that I can just believe it strongly enough to play with abandon from inside that character.