I've found visualising my setting an invaluable aid to visualising minor characters, where the main characters come from (and how they are thought of back there) and so on. If your created world does not seem real to you, then it won't to anyone else.
I've also found being able to visualise a starting point (a place, a character etc) leads on to visualising more of the Fairy Kingdom and its inhabitants. It's kind of like building blocks - you need one to start with before you can make a tower. And to get me started visualising anything at all, photos (my own and others I see) are wonderful sources of inspiration.