Set the healer as your focus
While focus targeting is usually the province of crowd control and Arena tricks, I actually set my healer as my focus target in the Battleground. It accomplishes several things.
Stick nearby the healer
It keeps me always aware of my healer. That awareness leads to better protection holistically.
It flags the healer on my minimap. I can't get to them if I don't know where they are.
It allows me to see their buffs and debuffs. If the healer has a mile-long list of poisons, I can assume she's getting jumped by a rogue.
It lets me select them more easily. I have bandages and off-heals. Having my healers as my focus target allows me to target the healer quickly to land those bandages in the right place.
If you don't have a compelling reason to be somewhere else, stay near your healer. Sure, if you have the flag, then you've got somewhere else to be. But if you don't need to be crawling up a flag carrier's skirt or trying to lay devastation on the enemy FC, your place is next to your healer.
Your healer needs to be capturing objectives and moving strategically just as much as you do.
Your healer will wander up to Mage Tower. No reason not to go with them. I'm not saying that you should stand in a road because that's where your healer happens to be. I'm just saying you should be clumped by the heals. Why?
Let the healer know
Enemies are less prone to attack groups. Battleground superheroes like to wander around and find lone, vulnerable targets. (What's up, rogues?) Standing next to your healer will discourage that tactic.
You're there to provide defense. While it won't happen quickly, it is possible for a rogue to kill your healer. If you're not on hand to attack that rogue in return, your healer will be useless to your team.
It generates goodwill. If your healer sees you actively working to be part of her defense, she's more likely to feel comfortable and willing to do her best in the Battleground.
You become a mini-god. Ever notice the derision people like to lay on "pocket healers"? Yeah, that's not because it's a cheap tactic. That's because a DPS/healer team in the Battlegrounds is powerful and awesome, and that other person is jealous.
If you're working hard to protect a healer, take the 10 seconds and make sure she knows it. This is because healers have a big job in the Battleground. Sorting out which raid members are in range of heals requires a span of attention that can easily keep anyone distracted.
It is entirely possible you could be connected to the healer as if by umbilical cord for a 20-minute match without ever being noticed. You're a raid frame to that healer. She's not watching the field; she's engaged in a vicious, no-holds-barred, every-second-counts battle of Whack-a-Mole where the stakes are life and death.
So take 10 seconds and say, "Hey, healer, I got your back. I'm not going to leave you alone." It makes a difference, trust me.
The rest of it
We could talk about a lot of other little tactics. Slow the enemy when they appear, use your buttons, do damage. But it really all still boils down to these three things: Make the healer your focus, stick nearby, and communicate. If you can do those three things, your healer's life expectancy will instantly go up. I'm not cheaping out on you and avoiding deeper tactics; these are
the deeper tactics. The rest is just deeps deepsing as hard as they can deep.
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