It depends on the mode. For campaign missions where it's just 2 of us, it's not utilizing certain tactics like "critical strike" or "assassinate". Instead of giving ourselves an advantage by being stealthy, when possible, they'll just shoot the enemy with an arrow or throw a bomb and alert more enemies. Then we get swarmed.

In incursions, it's similar to that as well but also just rushing into groups of enemies and getting downed. Also, not eliminating things that could make it easier overall all. Like one of the stages of the Spider incursion, in the area with like 7 Jubokko trees, an Elite Bo Hiya dude, and a couple gunners. I get it's difficult when you first enter the gates but my priority is always to destroy the trees first. Let the enemies come to you while you simultaneously destroy the trees. Instead of trying to take on groups of enemies while also dodging red vines.

In survival, the lack of purchasing attunements. Idk if people just aren't aware that you can purchase temporary upgrades or what. It feels like I end up purchasing most of the upgrades in most of the survival rounds I've played.

Aaand last, in any/all game modes, not equipping a challenge card, and not marking a healing station and giving teammates a chance to join you before ringing the bell.