Six Sigma for Dummies is a horrible book.
For technical problems (Six Sigma) try these in order:
Steiner, Stefan H., MacKay, R. Jock, “Strategies for Variability Reduction”, Quality Engineering, Volume 10, Issue 1, September 1997 , pp 125-136Moen, Ronald D., Nolan, Thomas, W., Provost, Lloyd P., “Quality Improvement through Planned Experimentation” 2nd Edition, McGraw-Hill, 1999
Ott, Ellis R., Schilling, Edward G., Process Quality Control, Second Edition, McGraw-Hill, 1975
For "lean" try some of Jeff Liker's books but the most of the best literature on Toyota Production System is in Bob Emiliani's blogs....probably the best place to start...remember that TPS applies to human based processes.