There is the newbie review website I was happy to discover as a noob, but it doesn't offer a whole lot and yeah, most material is pretty old.
Here are some basics that may sound silly now to the older players but that have improved my team's gameplay dramatically after a little mentoring (most of us played their very first 6s) :
- positioning meta for every map
- ad/disad concept
- passive/aggressive play
- purpose of a sac
- how to clear comms and what's important to say
It felt like a lot of the veteran players who coached us expected us to know this stuff but without clear guides in the wild there was just no way, so it was a long road until we managed to explain that when we say this is our first 6s and we don't know shit, we mean it.
And on a personal note I would love to see a series similar to rumpus's demo guide but for other classes.