The lesser known of St. Francis's books, Finding God's Will For You serves as an instructive discussion on how to navigate through life according to God's will. St. Francis de Sales is the patron saint of writers and after reading his book, it's easy to see why. It's amazing to see how he can take a profound concept, and simplify it through metaphor and other means. Furthermore St. Francis knows how to nurture your intellectual progress, initially spoon-feeding you the most basic notions until you are ready to handle some of his more advanced contemplations.
Many times a book will contain profound wisdom but be tedious to read. This is not one of those books. St. Francis will get you to think deeply about your life choices, particularly on the opportunities you have to conform your will to God's. Regardless of what God has in store for you on earth, it's His Will for you to be with Him in heaven. And that's all that matters.