I don't know sites on the net. Norm Lieberman books are good references in my mind.
Another excellent course is Kepner Tregoe's counse on problem analyses, decision analyses and potential problem analyses. I'm not sure it's still offered, it's been a long time since I took it but they have a very methodical approach to problem analyses that is very good.
It's key that you really understand how the system works from a first principle point of view because then you can start looking for and recognizing where it's not working as it should be.