Always finish your daily quest (but don’t necessarily focus on it as you play).
I know this but I am just so stubborn to actually follow it. And yeah this is really true as most of my loses are probably because of this. :)
Like when I get a Snipe Daily Quest and a 14 mana-cost battle with Water Splinter available. What I do is put Chicken at the front line followed by Pirate Sniper (Snipe) and then Ruler of the Sea. I am aware that this is pretty disadvantageous since when the Chicken is down my Pirate Sniper is basically useless but still I stubbornly insert that card to hopefully complete my daily quest FAST which usually just backfires. Lol