[1] introduced ordering in binary decision diagrams, [2] summarizes well the implementation techniques used in practice, [3] is the default reordering algorithm in CUDD, [4] is an introduction that doesn't assume any particular background, [5] is quite detailed and mathematical (by Somenzi -- the author of CUDD), and [6] is another, quite excellent, self-contained, and applied introduction to the topic.
[1] Randal E. Bryant
"Graph-based algorithms for Boolean function manipulation"
IEEE Transactions on Computers
Vol. C-35, No.8, August, 1986, pp.677--690
[2] Karl S. Brace, Richard L. Rudell, Randal E. Bryant
"Efficient implementation of a BDD package"
27th ACM/IEEE Design Automation Conference, 1990
pp.40--45
[3] Richard Rudell
"Dynamic variable ordering for
ordered binary decision diagrams"
IEEE/ACM International Conference on
Computer-Aided Design, 1993
pp.42--47
[4] Christel Baier and Joost-Pieter Katoen
"Principles of model checking"
MIT Press, 2008
section 6.7, pp.381--421
[5] Fabio Somenzi
"Binary decision diagrams"
Calculational system design, Vol.173
NATO Science Series F: Computer and systems sciences
pp.303--366, IOS Press, 1999
[6] Henrik R. Andersen
"An introduction to binary decision diagrams"
Lecture notes for "Efficient Algorithms and Programs", 1999
The IT University of Copenhagen