I hope that this kind of post is allowed. If not, please accept my apologies, I just wanted to post a plug for a great resource that I just came back from.
This last weekend was the first "Dungeon Master University" run by the DND in a Castle company. It was held in Atlanta and lasted 2 days, and it was an incredible experience and opportunity to learn from many of the best in the business. I got to take a Worldbuilding class from Keith Baker (creator of Eberron) and Monte Cook (lead director for 3rd edition D&D and worldbuilder of many many D&D worlds). It was an incredibly educational opportunity, and a hell of a lot of fun. Other classes included Skill Building, Campaign Design and Career Building. There were great seminars on how to run puzzles in great ways from the lead puzzle designer for many major adventures, and how to run games for high level characters from B Dave Walters (who is all over the internet for being generally great as a DM and storyteller) and Live Streaming by Chris Perkins (lead designer for much of 5th edition D&D who now works for Critical Role/Darrington Press).
There were "Game Labs" where you could run a game for others including a faculty member and get great in depth real time feedback and advice on how to improve as a DM. I got to play in a game set in Eberron with Keith Baker, and it was really fun.
But I think the best part of it was just wandering around and meeting dozens of other cool people who all had the same passionate interest in DMing as I do. I'm usually a really introverted person, but this weekend I had no problem just sitting down for dinner with a group of random strangers and immediatley starting up a conversation in a great welcoming community.
It's not cheap, but if you can swing it, I highly recommend it as a resource for becoming a better DM.