How do you go about diagnosing your brewing problems to find the cause? There are many online and book/magazine resources. I like using charts where I can scroll down a one or two page sheet to find some possible causes and then dig into some further research on those few.
Brew Your own (byo.com) has a great and (somewhat comical) troubleshooting chart aimed at new and experienced homebrewers. I keep this bookmarked for brewday and fermentation troubles.