In addition to the secondary sources listed below, there are rich resources within John Wesley's own work - particularly his journals and "The Characters of a Methodist." The General Rules were not static and it is possible to trace changes that were introduced over Wesley's time (and beyond).
Carter, Henry. The Methodist: A Study in Discipleship. 1st ed. Fellowship library. London: C.H. Kelly, 1914.
Davies, Rupert E.A History of the Methodist Church in Great Britain. London: Epworth P, 1965.
Nausner, Helmut. "The meaning of Wesley's general rules, an interpretation.." Asbury Theological Journal 44, no. 2 (Fall 1989): 43-60.
Watson, David Lowes. "Aldersgate Street and the General rules : the form and the power of Methodist discipleship.." In Aldersgate reconsidered, 33-47. Nashville: Kingswood Books, 1990.
"General Rules." The Encyclopedia of World Methodism. Nashville: United Methodist Pub. House, 1974.
Your further question about the literature of spiritual development can be addressed through several approaches due to changing terminology and definitions over time. The most current work in this area can be found by doing a subject search in our catalog or databases such as ATLA for "faith development." Also terms like "moral development" and "religious psychology" have been used to describe similar materials as well within the broader area of "Christian education."