I feel like world of Warcraft is very reliant on 3rd parties to learn and play the game, which may come as a frustrating and turnaway experience for all players in the game, not just the beginners.
It’s not too uncommon to see people complaining about learning their class at max level, or to see people being unfriendly to others still learning the ropes, complaining about people failing simple stuff, and most importantly it has become very hard to gauge one’s self progress and skill level because of how the game is built right now.
Therefor I’ve come with a suggestion to introduce a new version of the proving grounds that is entirely optional with the sole purpose of teaching people how to play the game and to be a cool self challenge for even the greatest of players.
I’ve divide the proving grounds into three sections and purposes that I feel would make them fulfil a good purpose and benefit for the player base.
Leveling
The proving grounds concept I’m proposing is something similar to the monk leveling experience when it first released alongside other extras.
As in every few levels the player as directed towards the proving grounds to do some tests and a cool reward is dangled infront of them to do so.
Starting from a very basic levels and focusing on pivotal skills people need the proving grounds will try and teach people how to perform in various environments and engagements.
An example :-
Every level threshold the player is invited to the proving grounds
At level 10 they are taught the concept of roles and their importance, party, playing as a team and keeping up with the group.
At level 20 they are taught the concept of interrupting, priority targets, and mob classification
At level 30 they are taught the concept of bosses, boss abilities and dealing with mechanics.
At level 40 they are taught about classes, utilities, quirky jobs and a simple form of dpsing, healing and tanking
At level 50 they are taught about positioning, deeper class insights, basic tips and tricks, fight dynamics, teamplay etc.
At level 60 they get an in-depth tutorial with a small challenge to teach them how to play the game and rely on themselves
Max Level
Once the player reaches max level, they are given multiple small tutorials followed by challenges and challenge levels that hones their skills and experience.
An example of this is this, dodging swirlies challenge.
Easy : A few swirlies, spawning at slow rates that players have to dodge.
Medium : A medium amount of swirlies, spawning at medium rates.
Hard : A good amount of swirlies, spawning at high rates.
Insane : A barrage of swirlies, spawning superbly fast.
After this is cleared, the player will be able to take on combo challenges.
For example an easy, medium, hard and insane combo of swirlies and battle simulation where CC is needed.
And once the player completes all of those the player will then have to take on an ultimate challenge that combines all of these things again at multiple difficulties were easy represents lfr, medium represents normal, hard represents heroic and insane represents mythic.
Self Challange
Once the player finishes all the tutorials they can take multiple challenges for funsake and maybe cosmetics that go deeper and deeper into mastering the game, introducing more complicated things and infinite scaling.
Challenges like M+ affixes, unique mechanics, multiple types of enemies, pack control, snapping and many more.
Think of this level, like students studying ultra hard math problems so that they can deal easily with the normal math problems you might get, so instead of solving 5x5 matrixes you can try and solve 20x20 matrixes, it would also be funny to have super ultra hectic encounter for the lols 
Ultimately, I think there just needs to be something for training, like the overwatch training room or generally fighting with target dummies but improved and there definitely needs to be some form of tutorials incorporated into the leveling experience and a starter and guide for players interested in improving their game and also a way to challenge players into achieving new crazy stuff.
I also really think there should be an emphasis on optional, as in having something forced upon you is wrong, which is why the original proving grounds failed, as long as there is a venue for learning and maybe a cool reward locked behind it ( not a mandatory reward ) then I think proving grounds would be a cool added feature.
I’m always surprised by the lack of experience shown by fellow WoW players in very basic things, and that is probably because there is no indicator to these things, unless someone tells you or you see someone doing it then chances are you’ll hardly learn it.
Things like imps LoS trick as demo warlocks, Using explosives as an energy resource on assassin rogues, using Shadowstep to escape as a rogue, leaping away from upheaval in Tol’dagor, snap spots and snapping etc etc, so many basic things that people don’t know about and I feel like there should be a learning avenue for that.