This is my "big lava" list that has been moderately successful across a few seasons of the Sorcerer's Summit, with a 55% winrate currently. That's pretty good in the Summit crowd of meta decks and extremely talented players, though I strive to hit 60% before Avatar of the Realm!
-------
Generally, you don't need to Fireball with Avatar of Fire. Threatening to do so forces your opponents into strange positions, and they end up making plays they otherwise would not to avoid getting two-(or more)-for-oned by a nasty Fireball down some line. I would say I cast Fireball on average 0.75 times per game, meaning the threat is more valuable than the spell itself! And people always assume AoF has to cast the Fireball; she doesn't! You can cast it off any Spellcaster, many of which I have included.
Despite not having to Fireball to do well with the deck, you do still generally want to give yourself as many opportunities as possible to Fireball when you really need to, because nothing is more demoralizing than yeeting a Fireball into someone that the just brazenly walked into because they forgot she has an ability at all. To that end, I have found that 8 non-fire sites is tolerable for maximizing the chances of hitting earth threshold while also being able to reliably Fireball. What those 8 nonfire sites are is up to you, but in the current meta I like having Pebbled Paths, so I don't run Charge minions at all. Gnome Hollows could be switched for something else probably, but I find that I like the lanes it shuts down for the majority of the opponent's minions. It also means you can't defend it super great without Root Spider, but the combination of those two is generally pretty hampering. Rift Valley is generally pretty useful and could be another option for you, although I think it's a bit less good for AoF since you can't play it and also Fireball in the same turn.
-------
Anyway, generally you want to play as few cards as possible, slow the opponent down, then take them out in a few big chunks.
I'll keep updating this list and Primer a lot as I continue on my journey.