Here's another rich seam of OSR material my mining of the old school blogs has turned up. I suppose I should sort all of these links and ideas into a structured and coherent guide at some point.
Hack & Slash goes into the Quantum Ogre and why Illusionism is bad. The Alexandrian explains what Abused Gamer Syndrome is and how to fix it.
The Blorb principles @idiomdottning.org are for prepping old school adventures.
Then @SpiderQueenGaming, Ed, has some OSR wisdom here:
And some more practical advice here:
Finishing off with 8 Lessons from running a successful sandbox.