Switch Often, just because you called the restoshaman 10 seconds ago do not be scared to call for a hard switch.
Enable „Target Count“ in your Battlegroundtargets add-on. This will allow you to see how many targets are assisting your target.
Call for CC on healers when you are going to burst
Give countdowns, for example. Say: 5 seconds till AOE grip (via gorefiends grasp). The most important thing here is that you need to check for your teammates cooldowns, if you can line up an AOE grip with an ursols vortex, ring of frost and Solar beam, you can wipe the enemy team in seconds, getting this properly coordinated is fairly hard though, and will cause you alot of stress in trying to set up, even on high level, but it is definately worth it.
Grip overextended targets even further away and call the kill for them.
Use battlestandarts, place them on places behind team, kill enemy battlestandarts asap(even healer can do that pretty easily).
Loot enemy corpses so they cannot ress.
Stick together! Follow call orders.