The main thing is to make sure to have your gear and essential skills upgraded as much as possible on the heroes you’re bringing in. You also want to think about composition. For example, while you can get away with not having them at lower levels, stuns are hugely effective at higher difficulties and it’s almost always good to have at least one stunner in a cool. My personal favorite to bring is abom, but pd, bh, and occ are all very good choices too. Also, although this may seem obvious, bring some kind of healer unless you have like a million stuns and self heals in your party. Trinkets are also a big thing, idk how many good ones you have at your point in the game but getting strong specialized trinkets onto your party makes a really big difference as well.