Crowley, like most spiritual teachers, recognized that one's Will is generally buried beneath a thick layer of what can be called Individual Ego—the conscious sense of "I" that feels separate from the Universe and is a complex mix of beliefs, values, and norms derived from socialization and various life experiences. A Thelemite is therefore one who seeks to break through her "conscious programming" in order to reconnect with the secret self, thereby becoming aware of her true, unfiltered nature. This process is called the Great Work.
The techniques used to accomplish this difficult task fall under the general term Magick, and traditionally include practices such as yoga, invocational ritual, and astral body work. In more recent years, Thelemites have been starting to include other, non-"occult" methods to accomplish the Great Work, such as transpersonal psychotherapy, hypnosis, and isolation tanks. In the end, it is up to the individual to find the doorway to her own inner self.
Books You Might Enjoy:
William Wynn Westcott - The Sepher Yetzirah
Tuesday Lobsang Rampa - The Third Eye
Tuesday Lobsang Rampa - You Forever
Aleister Crowley - Gilles De Rais The Banned Lecture
Tarostar - The Witchs Spellcraft Revised