When it comes to a custom UI, information is king. Sure, there are ancillary benefits, like the pursuit of a pretty user interface, or a minimalistic one, or (be still, my beating heart) both. But when you get down to the real meat and potatoes of building a UI, the most successful are the ones that are most effective at presenting information to the player in an efficient and useful manner.
And of course, many players are perfectly happy with the stock UI, which is totally fine if that's your cup of tea. For many others, myself included, the preference is for a custom viewport into Azeroth that can distill everything at your disposal into a package that can be quickly digested by the brain, as well as all sorts of bells, whistles, and dinglehoppers that make for a more aesthetically pleasing interface. Because that's half the fun.
But what kind of information matters to a tank? I can think of five kinds of information I want to be as tapped into (Matrix-style) as I can possibly be when tanking. They are as follows.
What do my hit points look like?
Knowing your current health is hugely important to a tank. We use that information to make a multitude of decisions, from when to use a cooldown or a trinket's clicky effect, to when to panic at the healers in Mumble for not healing us fast enough. A low health number gets the adrenaline pumping, fueling a bullet time-like effect that slows everything down and compels us to react decisively to whatever is threatening to end our avatar's fragile existence.
There are multiple ways to efficiently display your health information, and anyone who has looked at or used custom UIs has likely seen a dozen examples from horizontal bars, to vertical ones, to percentages, and so on. The key, though, is more where the information is on your screen. Stock UI puts your hit points tracker in the top left of the screen, which means that (depending on your resolution) you're likely going to have to move your eyes to catch the information, potentially breaking your concentration over what's happening in the background.
Instead, you want your health numbers somewhere off of the middle of your screen -- not immediately in the middle, mind you, but in a place where you can still see it within your immediate peripheral vision while looking at the center of the screen, where your character is. There's a sweet spot that shifts from person to person.
What about my resources (mana and holy power)?
Similar to how you want to display your health information, it is important to have an immediate view of the current state of your resources, both mana and holy power (though truthfully, the latter is far more important than the former these days, considering how free-flowing mana is).
Holy power, nonetheless, should be presented in an easily digestible, convenient way. See my screenshot above for how I do it. Three icons, right next to my health -- my brain immediately knows the status of my holy power. This prevents excess latency between the ascertaining of how much holy power I have and then the use thereof.
What's my damage intake look like?
I generally hate clutter, but the one information overflow I can't live without is a scrolling battle text mod (like MSBT) set up to display my incoming damage on one side and my incoming heals on the other. It doesn't have to be garish or overly intrusive, but it should be some kind of reliable feed of the stream of hit points entering and exiting my bars.
That way, when you're tanking, you'll be immediately aware if the boss is on some kind of a big-hit streak and can react accordingly. Again, it'll spare you the lag time of looking at your hit points tally and having to do the internal math of how quickly you're taking damage. Just be sure to keep it tasteful, however you choose to display it.
What's on cooldown and what is not?
Especially when it comes to your survivability cooldowns, it is absolutely critical to have a good view of what the availability of each of those abilities is. When you're facing off against a deadly boss and spy on your (conveniently located) health indicator that you're in trouble, you don't want to have to stumble to figure out whether Divine Protection or Ardent Defender is off cooldown or not.
So, much like the idea with locating your other indicators, you want to keep your survivability cooldowns somewhere that the eye won't have to jaunt too far to reach.
More offensive abilities are less critical -- you're not going to go splat if you dither for two seconds discerning if Hammer of Wrath is available yet. As such, I tend to push those off to the bottom, where they won't clutter the more valuable real estate.
I also have WeakAuras set up to show various buffs or debuffs (depending on encounter) and whether they are up, or in some cases missing, or in other cases how much time they have left on their duration. It's a much more effective way of transmitting timing information than checking out my buff/debuff icons at the top of the screen and mentally parsing those. (Again, the keyword here is keeping any auras tasteful. It's easy to get carried away.)
How to get as much of a view of the field as possible
That said, the biggest caveat is as I alluded earlier: Don't overdo it. You don't want to crowd the center of your screen -- the most valuable real estate in your interface -- with a lot of elements and flashing lights. The more that's infesting that critical area, the less space you'll have to be able to see all the interesting and deadly things going on around your character. Void zones, and the like.
Keep icons and elements as small as possible, to the point you don't have to squint or scratch your head to figure out what the hell they are indicating but not so big that they are potentially crowding the field.
Ultimately, your screen is like beach-front property on Martha's Vineyard, and your UI elements are like senators prepared to slap-fight to the death for the most valuable lots. And even more importantly, do remember that information is key, and knowledge is power. The more information you can ascertain and the faster you can process it, the more intelligent your decisions will be.
The Light and How to Swing It shows paladin tanks how to take on the dark times brought by Cataclysm. Try out our four tips for upping your combat table coverage, find out how to increase threat without sacrificing survivability, and learn how to manage the latest version of Holy Shield.