Aatma Gyan Prakash is a good book on Aatma Gyan. This book consisting of very easy remedies of how to find god in ourselves, some meditations are also given within this and the ways are been depicted of how to be simple and effective.
Shiv Swarodaya is the basic scripture on the science of breath. It is one of the tantric texts belonging to Hinduism, also termed as Swara yoga by Satyananda Saraswati. It is also termed "Phonetical astrology": the "sound of one's own breath". This is the very basic book on Swar Gyan, given with the Hindi Translation.