Hm, Im no expert sir on the subject but I'll tell ya how I went about this one. Basically I looked at the things on the face that stood out the most to me. The nose, the ears, the strange shape of his mouth, then I over-exaggerated them, which makes it all look really funny. I would do a search on youtube for "caricature tutorials" and watch a bunch of those. That should lead you in the right direction.