I usually throw beginners directly into full games of arena and start this with explaining an overview: Idea and goal of the game (mages fight to death in the arena with different strategies), that mages and schools are different, that you pick cards from a normally self-build spellbook and play thorough phases.
Then I show starters the 4 prebuild core-spellbooks and and what types of cards are in there and how those mages feel like without any detail. After about 10-15 minutes we are here and they choose a mage.
Then I go through the setup, symbols on the cards, phases and boardmarkers and some basic strategies (rush, swarm, economic first, trying to get mana and/or action advantage).
From there on we play a semi-secret game. For sure there are many questions about keywords and rules and I will see my opponents book and cards to explain. So I pretend (also to myself) I don't know what my opponent is planning. When he or she made mistakes I let them switch cards or rethink the idea (fireball on burnoroof, shoot through wall, melee-only-defense instead of anti-ranged). The game is completely vabout getting the feeling of what is possible.
This way it is fun and has a manageable learning curve. I can try out some new openings so it is not boring at all. So far I had a very good experience that way. The main point is: let them play and help just when needed in a gentle manner!
