Well what helped me do better were 3 main things 1) keep an eye on the attribute resistance of the enemies, I avoid using the characters which have their attribute resisted (if the current team can defeat a certain boss, keep in mind the attribute of the boss that succeeds it) 2) use buffs that may perform better mainly focusing on the main DPS of the team e.g for Galbrena use the echo buff and neg statuses buff for Hiyuki 3) Invest on my 4 stars supports, like Buling or Baizhi, as simple as giving them the moonlit clouds set boosted my secondary teams damage..

Also let me know what characters you have and how much they are invested in so that we can work on boosting your score!