Note: if you are trying to heal low level dungeons, you can just swap the shaman to elemental for those. Or do what I've done in the past: make a macro (on the tank) saying you are rusty at/new to tanking and to please follow skull markers (keybind marking skull). Then let people die that pull threat. Most low level dungeons won't really require healing people who aren't the tank as long as they aren't being dumb.