Seeing as the head is at the top of the body (usually) we started with that.
All poses may not be as active so here is 'leading with the head' a little more naturally.
Just like the song, "Head, Shoulders, Knees and Toes", shoulders are next. Shoulders tend to be pretty aggressive if you think of breaking a tackle in football or body checking in hockey or a space warrior babe alien thing.
But shoulders also act as shields to try to protect feelings or the spirit inside as in the case of a shy person as suggested.
Next most logical body part to lead with is the chest. This may be considered the "being on display" pose, the look-at-me walk etc. Leading with the chest can express confidence, superiority, heroism, confrontation etc.
Working our way down, we get to the stomach. I going to digress for just a moment and say, I had a room mate, a well fed room mate, back in college who lead with his tummy. If you were having a conversation (or doing any sort of activity) The tummy would arrive first, leading the 'mouth' which would drop whatever opinion the room mate had at the time. Below are just two examples of stomach lead.
Which brings us to the pelvis. All of us, at some time place our weight on one foot shifting our bodies into a contrapposto position. This is a form or leading with the pelvis and there are lots of methods to this type of leading, four are below:"What about twerking?" "Ahem...yes that is form of leading with the pelvis...but I'm not going to draw that." "Ahh." "...Um try this."
Leading with the knees tends to push the body backward awkwardly, this is great for describing a lanky or under-exercised figure. But, if you look at people taking a photo on their cell phones, they tend to lead with the knees to try to angle the body back to get more into the shot. If you look at "the Lovers" from Commedia del'arte, you will find that these characters (who usually lead with the chest) may fall back to lead with their knees when they stand still and let the warm emotions of love and happiness wash over them. Same is true of people who are experiencing a true emotion.
Leading with the toes lightens the character's movements. A sneak, sashay, or sexy walk (though a sexy walk also is a lead with the chest and shoulders as well) are examples of leading with the toes.
"Can you lead with your arms?" they ask. Of course! Leading with the arms of hands gives purpose to the intended action of the appendages and they really to have a reason to up. It's very hard to sneak with the arms up as it places you off balance, in this case, arms are better positioned near the core of the body to act as ballast. A high dive is an obvious lead with the arms/hands, entering a dark or smokey room would be cause to lead with the arms/hands to prevent collisions with unseen objects is also a good use of the arms leading.More on leading later, for now think about what your character would lead with and continue to push your posing and animation. Thanks for stopping by!