These are the things new players have been told for years and they pop up in every thread like this one:
You can practice offline.
You can watch YouTube videos.
You can read about it on the website.
You can go to the forum/BBS.
You can get with an AH Trainer.
Note that the expectation is for players to leave what they are doing (or exit the game!) to figure out how to play the game. This is the old way. It has been ineffective in retaining players and is not how most games handle it.
The clipboard GUI, literally the first thing players see when entering the game, is old-looking and not intuitive. At least 80% of modern (especially online) buyers make a decision about a product in the first few minutes based on what they see alone. What do you think most players' reactions are when they see the first clipboard pop up? Beyond that, there are no clear set-up instructions. There are no in-game tutorials or easy methods to test and modify their setups. For the majority of people, if they struggle and can't figure out how to solve these issues in-game, on their own, intuitively, then they are gone.
If it were up to me, my focus would be to first update the GUI and add clear tutorials with "rewards" of some kind (if only positive feedback!). Start with clear directions to set up their controls, change key-bindings and fly (with an air start!) to test out their controls and clear instructions to exit if they want to change them. Then show them how to customize their aircraft with fuel load, armament, ords, convergence and skins! Then work on progressive in-game tutorial missions in the aircraft of their choice -- Lesson 1 (airstart): "Follow the C47... good! " Lesson 2: "Follow and shoot the C47... good!" Lesson 3: "Take off, shoot the drone and land... good!" Similar things could be done for GVs and CV task-forces. (i.e. A successful carrier take-off and landing unlocks a new Navy skin.)
I'd do this BEFORE you give new players competitive AI or other players to shoot at. Make the AI difficulty player-selectable, easy, medium or hard in the mission screen (like Warbirds had in their practice missions, IIRC). Maybe unlock more simple things, like more skins or additional aircraft choices, for completing the tutorials or winning dueling missions against AI in different aircraft at different difficulty levels. There are lots of small positive rewards that can be given in the free arena, providing players with a sense of progression, before throwing them to the wolves of the main Melee Arena.
Competing in today's competitive marketplace requires ease of use and some immediate gratification (the "small shot of dopamine", as was perfectly mentioned above) and this would be a good formula for that.