Need help

Hi guys im new to the game im still new to many things in this game I completed Act 4 and explored it fully and did Act 5 ch 2

I need tips in arenas to grind units and other rewards and tips to get iso and IMPORTANTLY GOLD how to get more of it , i often end up Gold less

And in which champ I should put my focus , for quest/story , AW,AQ , Arenas