There is so much literature out there with regard to mediumship training/development, spirituality, etc. etc. - all topics covered by Sylvia Browne. Seek and find what works for you. She may be what is right for some, but not for all. That is the nature of development - seek what works for us in our own way.
If something does not make sense to us, then it is not for us - if it resonates with the heart - it is right for us. Choose wisely.
Strictly Mediumship development, best book I found - Develop Your Psychic Powers by Tara Ward found at
www.abebooks.com (new or used)
Spirituality often comes from a religious following. Spiritualism....A Way of Life by Elizabeth Harris is a good volume for spirituality ideas.