I see too many times that people don't even know what they have in their closets. Before you can build a wardrobe, you have to know what you are working with.  Some may need a small amount of additions to their closets and some may need a lot, but you won't know until you take the time to evaluate your closet.  Take a weekend and go through what you have.  Grab a notebook and write it down.  You want to make columns in that notebook for tops, dresses, pants, skirts, etc.

Make a column for staples, as well. Staples include items like flare skirts, pencil skirts, button up blouses, denim, etc.  This article from Real Simple Magazine gives you a list of closet staples.  Once you have this list of things you can evaluate what you need and what you don't.