Treat each wave like a timed pull
Set tank pickup zones and kill priorities before the event starts. Ranged players should know which dangerous casters or flying enemies they own, while melee avoid dragging threat through the back line. Do not spend every cooldown on an easy wave if a harder combination is next.
Time between waves is recovery time. Resurrect quickly when possible, drink immediately, rebuff only what matters and be in position before the next pack reaches the raid.