Here's a little insight into how I like to work. I did a rough sketch of the T-Rex in my sketch book with a good old fashioned col-erase pencil. Then I import the sketch into flash and put him with a cleaned up character, so that I am working with the correct size relation. Then digitally sketch over the scanned pencil sketch. I will sketch all the expressions and poses needed according the storyboard, and then clean and color it.