The classic sefer Tomer Devorah was composed 500 years ago by the kabbalist Rabbi Moshe Cordovero (also known as the Ramak). While the sefer as a whole is deeply mystical, the first chapter at least is quite accessible, even practical, in exploring the 13 qualities of Hashem that a Jew should learn to emulate. It becomes even more practical now with the addition of Rabbi Avigdor Miller's eye-opening Ohr Avigdor commentary.
(As the later chapters of Tomer Devorah are too lofty and mystical for the typical reader, the Rav's five recorded lectures on this sefer were limited to the first chapter; the Ohr Avigdor Tomer Devorah is complete in this one volume.)