Hmm, necro but a good one.
Surprised to see only one mention of The Alexandrian. To me, it's by FAR the best, and if I could only pick one, it would be this hands down.
Welcome to The Alexandrian!
thealexandrian.net
Absolutely amazing stuff. So much of my approach to running a game is from his blog. He started a YouTube channel recently as well.
His tips on running a sandbox, how to handle mysteries, giving clues, etc are priceless. His blog has been around a long time so there is a wealth of info. This is one of my favorites:
If you're GMing a roleplaying game, you should never prep a plot.Everyone's tastes are different. These matters are subjective. What works for one person won't necessarily work for another. Yada
thealexandrian.net