4. Fill in the gaps

Sometimes your tank sucks, or you have a bad pull. It happens. When healer pulls aggro, be ready to off tank. If you see the tank reacting immediately, carry on. Sometimes they are oblivious, and while the healer is too busy healing himself, the tank's wondering why he's not getting heals. Sometimes they expect White Mages to put'em to sleep, while the healer is juggling priorities in healing. That's just lazy tanking.

You have to fill in the gaps. Protecting the healer takes priority over dps. As soon as you peel it off the healer, go back to attacking the primary target while leading them back to the tank. If you have any defensive skills, this is the time to pop them.

Closing Note

You meet a bad tank, deal with it, change it up, and make it work. That's your true role in the group.