Dress for Success by John T. Molloy is pretty helpful, if dated. For the most part, it's still very applicable even today, if you ignore the sections on trends and dressing for women. The examples still look pretty tasteful and classic. It's particularly interesting for trying to dress for specific purposes in specific geographic regions, especially if you are built nonstandard. I personally am someone who is a visible minority with a small build in a peculiar social group as a student leader, so I need to be very careful in dressing well but appropriately. I came up with my solutions on my own, but reading Molloy's book after-the-fact made me realize why what I chose works, and what would work for others and for myself in different circumstances. It is also helpful for people trying to dress on a budget, which is great for those just starting to build a wardrobe.