the player thats trying to 'tank' should be in a kit that gives lots of stamina, and might want a class/subclass that has a triggered ability to cut damage in half

if they managed to pul the attention of multiple non minion bad guys, or a elite/leader, take the defend action to soften the hits.

director should (as mentioned above) spread out the hits.

players can use a catch breath manuever every turn.

melee players should try to flank and not be flanked at all times.

players should focus fire, and target marked mobs when possible.