Reading a book or taking a course plays a small role in your way to being a database designer. Touching the problem, getiing your hands "messy" with database modeling is what will make you a good developer. My grandma (may she rest in peace) used to say: "If you could learn just by looking, then the butcher's dog would have become a butcher by now...". What she meant by this was, that one needs to gain the knowledge by experience and by his own curiosity.