Most of the time when I design jewelry, I am simply designing around a pendant or focal point. I pull together the colors from the piece, or I bring in a new color, and I focus on complementing the central element in the way I think best suits it. There is no "audience" for the piece, so to speak; other than general thoughts of how one would wear it, durability, ease of use, etc., there is only a faceless person on the other end from me that represents the owner-to-be.
Sometimes, though, I make jewelry for someone specific.
I found these paper beads in a store, and immediately thought of a friend of mine who loves Boston Terriers. And I bought the piece and decided to keep it very simple. She is an active person, someone who does not like a lot of fuss in her clothes or jewelry, and so I kept it streamlined and put a toggle clasp on the end so it would be easy to put on and take off.
You know, I've made some complicated pieces of jewelry for family and friends before, pieces with a lot of movement or wirework, and then often I see them wearing the simpler pieces much more often--pieces I would never have imagined they'd like more than the other, more complicated necklaces. It's intriguing to see which jewelry becomes a standard part of the wardrobe and which jewelry is only an occasional addition.
Part of the fun of designing for a specific audience is that I can picture the person wearing it, and that influences the design process.