Here's the single one resource I'm giving any of our new leaders, it's really short and the highest signal-to-noise ratio I've ever seen:

https://www.defmacro.org/2014/10/03/engman.html

I'm personally revisiting it every time I send it around, because it's just so good.

Here's another I've seen recently that goes into a bit of detail while not being quite as succinct:

https://news.ycombinator.com/item?id=30240428

EDIT: replaced second link with HN one as it contains an Emoji and broke due to policy