Continuing on from a now defunct project (atleast for me) Its a fine Line as to knowing what people want, to what they actually get. I try to sketchout Ideas on Paper using the description they give and then show them to clients. Using Bits and Pieces of what they Like while discarding any unwanted stuff and filling it with the new and continue with this until Eventually you have a character close to there vision.
However Sometimes you are expected to get it right first time, and this is hardly the case. Especially for Major Characters, while creating Extras a Much less Insignificant Character you have a lot more Room to Move.