Sort out your stack resolutions
I played a Deadly Dispute in response to an opponent's Check for Traps. My spell resolved, drawing me a Dragon's Breath. I could have used it to kill his Lier, Disciple of the Drowned, as I had an Inferno of the Star Mounts in hand. However, it immediately let him resolve his spell, letting him force me to discard Inferno. There should have been another round of priority between resolutions, but because I had clicked resolve (not even resolve all), the game never gave me a chance to cast it.
Basically, Arena doesn't even consider that people sometimes want to hold priority and respond to their own stack items.
It's design flaws like this that lose games for people, and makes me extremely annoyed. I don't have the opportunity to play paper Magic where I live, and I'd like to enjoy the game but Arena makes that very difficult. It's not even the players' constant net-decking and playing the latest fad, it's the platform itself!