I've probably spent 85% of my D&D time as DM, but I have very rarely had the opportunity to pick the brains of other DMs at length. YouTube has provided an invaluable resource for D&D players; especially DMs.
There are a ton of quality channels to learn from. Per the recommendation in this thread, I'm going through Colvilles channel right now (on video #23) and I love it. I could do without his intermittent and obvious SJW remarks, but I've still learned a few tricks for mechanics that I used to handle in a less elegant way.