Start with head, hands or facial expression not ROOT
I don't know if this works for everyone but I came up with some tips for animating William since after I learned layered approach. What I found it the most interesting thing was to start with the BIG movement, and which is kind of interesting for animating the particular type of character like William. He is really stiff, and spine is aligned pretty much all the time, it seems to mean the biggest movement is not ROOT but maybe head, hands or even facial expression sometimes look bigger.
Whenever I was asked "What is the biggest movement?" "Which part of the body does start moving first?", I tended to say ROOT even before I think about it. I think this is one of the reasons why animating William is so difficult (at least to me). It's easy to be off model if William moves his spine as we move usually.
So I tried to start with big ones not ROOT as I used to do all the time. There are a lot of different approaches and personal preferences, so I don't know if this works to everyone, but anyway, it works to me to avoid moving the spine too much.