I finally got around to doing the heckling hare exercise John posted. First I started figuring out the basic forms and angles like John said. (although I still didn't get the dog's cranium tilt right).
Next I redrew the forms and started building the characters from the ground up. I had a bit of trouble getting Bugs' muzzle right because I wasn't squashing and stretching it the same way as the frame grab, but I think I fixed it.
I haven't yet gone back to identify and correct all the mistakes, but right off the bat I can see that the dog's cranium isn't tilted enough, and Bugs on a whole is too elongated. The right side of Bugs that's supposed to be squashed is too low and looks a bit saggy. Everything on the right needs to be raised up a bit to get more of that exaggerated feeling. Bugs' neck tapers a bit before it connects to the head, when really it should flair a bit. Also, I didn't realize until I started to add the extra details, but the dog's head is way too narrow and his teeth are a little too small.