Well there is this guide, but for advanced stuff that completely not rlated to melee games, like Hero Arenas, I would suggest triggering it. Can be a little hard, but can act like an actual player if you really put your efforts into it.
I suggest just start triggering it, and if you encounter problems - ask here
Just like what i said in the title, how to make a Ai system for my hero arena game. From picking heroes, buying items, learn skill and casts spell attack / retreat.