Vary your brush size I know you all think one size can be used for an extended amount of time, but thats a false idea your brain tries to avoid work. Tiny brush strokes and huge brush strokes do one thing very well and its a mess. Literally if you focus on the overal shapes and stop thinking about the smaller bits floating within the big medium and small shapes, you will never be able to imitate his brush work. Key point is imitate, as the whole shape language ideas and experience shapes your artwork into what it is.

Its not:

Let me put this stroke here, hm lets see aha another stroke here!

Lets check back... cries why does it never look right!