I get stuck drawing the same kinds of faces sometimes, especially when I have so little time to draw. So I do these iterative practice pages to help get used to changing details, small and large, to change the look of a face. Check out Sycra's video - Iterative Drawing - The Fastest Way to Improve.
It's funny because I see several old styles that I used to do - different stages of drawing. The top right was definitely a phase I had in 2004. But the middle right is definitely my current mood.
with love - M