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Your options are be good at h2h and grind out super bowls, spend money, or work the auction house.
For most people, working the auction house is the easiest way NMS unless you're a god at h2h.
I noticed buying on Thursday, Friday or Saturday and then selling when the prices rise back up after that cycle seems pretty reliable if you have a high risk tolerance. You can make playbooks and sell them if you have a low risk tolerance but high boredom tolerance. I like to just play because even losing in seasons gets me pretty solid coins. I do look at objectives so I have goals and occasionally do solo battles or challenges but those are so mundane.
Buy in the auction house when prices low and sell high. Once you figure out ways to do it, it's not hard. Just tedious if you don't enjoy these sorts of things.
Pretty much what BreakLuna, AntiTwisted, and McCullersGuy said. Not much else you can do to make coins other than what they've already said.
Buy LTDs when they are still in packs and at their cheapest point. Once out of packs watch for a higher price point and sell them. You won’t get rich off 1 but doing this multiple times will add up. I’ve bought and sold every LTD so far. Nice way to store coins. Also don’t chase all the new cards right away. Problem I have faced in past Maddens. Be patient