I really like Neil van Niekerk's book on using speedlights. I believe he also has a book on off-camera lighting, and I would definitely look into it and check out his website. He's good with lighting patterns.
Strobist is good for technical advice. I'm not a regular reader, but have read info on the site a few times.
An undeniable paradox: To think that there is any such thing as an absolute rule is at worst naïve, and at best, shortsighted. There is no such thing as an always-true, all context- or situation-salient, absolute rule that always holds true including this one!