Apart from the hat he's quite a simply dressed figure, and he has straightforward hair, but a lot of character in his face is created with his eyebrows and beard. I didn't give him a smile, because he's a tough-guy sort, but you might want to make him looking happier when he's wearing that hat!
I experimented with two versions of the hat, one made the normal way round, and one made inside out to give a different texture that maybe looks a bit more like knitting. I couldn't decide which one I liked best, so you can choose which you prefer.
I'm also selling the Mal and Jayne patterns together at a reduced price if you want to make them both, on Etsy and Ravelry.
I've got a couple more projects I'm working on right now, but soon I'll get on and design the pattern for another Firefly character - I think it'll be Kaylee next.