OK, this isn't actually a guide on how to play retribution as there's some guides out there that totally blow away anything I could write up. Instead I'll just link to those guides and provide some useful info that ISN'T in those guides. To start, you simply can't beat the Elitist Jerks forum for any class questions, and specifically the Retribution Concordance (currently updated for 4.2 at time of writing). All the information for how to play, what to spec, and what stats are best and worst for you are here, definitely worth the read.
Now, even with awesome guides like that I've seen a lot (and I mean a LOT!) of people complain that retribution is hard to play and they suck at it. Every time i see this, my first thought isn't that it's difficult to play or that they're bad players, but simply the information you need to properly play is scattered to the 4 corners of the screen. Quite literally! Your abilities are all along the bottom and sides of your screen, your holy power is in the upper left, and the inquisition buff is hidden with the rest of your buff in the upper right. Default blizzard UI = crappy ret pally. Even me, I SUCKED the few times I tried to play on a friend's computer. So what to do? First things first, read up on your class above. Next, grab yourself some addons buddy!
With that understanding of WHAT to do, the clincher to playing ret is WHEN to do it. When do you Templar's Verdict vs use Inquisition is the biggest one. Ideally, you have Inquisition up 100% of a boss fight. But that's not always possible, and it's hard to track effectively. There's 2 ways to get around this. CLCret is a good starter addon. It tells you what ability to use next for maximum single-target dps. It doesn't actually use the abilities for you, just tells you the ideal one to use next. It's very helpful, but I suggest only using it long enough to get a feel for when you should be using abilities, I don't like being constantly told what to do. It feels like the addon is playing for me, instead of telling me information and me making those decisions. But, the very beginner can stop reading this guide right now, it'll still be here when you come back.
For the real meat of it, you need brace yourselves for some ugly. This is my (extremely cluttered) UI with all my addons running. Brace yourself...
Pretty bad, I know. You can see I'm in the middle of a Hex Lord Malacrass fight in a random Zul'Aman 5 man group, and I've just popped all my major dps CDs. Well, you could see that if you could make heads or tails of the info on my screen, so lets break it down.
First and foremost, despite the clutter you'll notice all my essential, important info front and center highlighted in pink, blue and red. My health and mana bars are to the left of my character, but more importantly my Holy Power is right underneath my feet, so I can watch it while making sure to not stand in Bad Stuff. Right below Holy Power is my major buff timers for Inquisition and my DPS cooldowns, and below that at the bottom of my screen is all my abilities clumped into one nice big cluster, so I'm not searching the 4 corners of my screen for abilities. Everything I really need to watch is right there in the center of the screen, near my character so I can watch positioning. These are the essentials you need to play ret effectively, the rest is just stuff i like to be able to see at a glance, in my periphery.
iceHUD for one major reason: the holy power. The health bars are nice, but it's the holy power (and runes on my DK) that i care about. X-Perl can do the same thing if you want a party frames addon but not the health bars, and there's other addons out there as well, but again what is important is moving Holy Power being somewhere so obvious you know how much you have at at all times. Ret uses a priority rotation and the biggest deciding factor in that priority is how much holy Power you have. It determines everything, when you refresh inquisition, when you can TV, when you should pop zealotry, when you should skip CS at times. Everything. Holy Power tracking is key to this, so make it obvious.
TellMeWhen is an amazing, highly customizable addon for any class. In this case it's used to track Inquisition (as well as a few other things). It gets set up right below Holy Power because upkeeping that buff is incredibly important. TMW is very similar to Power Auras and is pretty much completely interchangeable. The main difference is TMW shows an ability icon with optional timers instead of a glowing symbol. Either addon will do the same thing, but I prefer TMW by far. Use it to track buffs/debuffs/procs/status effects you want, or to track when multiple buffs line up, or any number of stuff. For tracking Inquisition I have it set to show a timer and it glows big and red and angry if it's not up, but is hidden outside of combat. In the screenshot above you can see I also have it show my durations on Avenging Wrath, Guardian of Ancient kings, and Zealotry (which should all be used together for max effect) so I can see at a glance how long I have left for burn phases. Ret is very dependant on these CDs and mismanaging my abilities while they're up, activating them at the wrong time or even just poor luck with procs can have a HUGE impact on DPS.
Dominos action bar addon. This barely made the essential list, but again it puts info you need (your abilities) front and center, and keeps you from having to look around and move your mouse across your entire screen. Abilities I have hotkeyed are on the bottom, abilities I click the most are at the top, and rarely used abilities are in the middle. Bartender4 is another addon that does the exact same thing with one exception: profiles. Bartender requires a custom setup per character, Dominos will save button positions to a profile set that any character can then load. Amazingly important when you have alts (and boy do I have alts!)
Deadly Boss Mods. Do I really have to say why? It tells you when important things are happening during encounters. If you don't use it, you're not going to be as effective in fights. Period.
X-Perl Unit Frames and other unit frame addons are awesome. Not QUITE as necessary now that the default raid frames are pretty nice, but X-Perl displays some very useful info. Most importantly, you'll notice the Boss frame has a few large debuffs next to all the smaller ones. Those are mine. Not as important for ret pallies as other classes, but it means I don't need to use any kind of DoT timers on my DK or hunter. Another great thing is it shows target of target for every party member so I can see what people are attacking. Lots of other info like curable debuffs can be shown, or when members are out of range etc, but mostly it's a DoT timer with extra info is why I like it.
Omen and Recount. Omen is mostly for tanking actually, the built in threat meter is ok for DPSing. Recount is almost essential though. Not for linking meters to stroke your Epeen, mind you, but as a measure for how you're doing. I always run it, and I'm always comparing how I'm doing to how I've done on fights in the past. It's a great tool for self-improvement and for figuring out where you or others might be making mistakes. Just don't abuse it.
Healbot. Or Grid+Clique, or VuhDu. These addons could easily completely replace your raid/party frames if you want, clearing up screen real estate. "But," I hear you say, "You're a RET paladin! you DAMAGE stuff, you don't need a healing addon!". ORLY? Healing addons are awesome for ret, for a few reasons. They let you throw out easy Word of Glories and Lay on Hands without target swapping (which can take precious seconds) . They track curable debuffs so you can cleanse with a click. You can set them up to use your Hand abilities with a simple click of the mouse without having to target the player then click the ability that you probably don't have hotkeyed. What's that? Adds wreaking havoc and the healer has aggro? *click* -Hand of Protection- *keep DPSing like you didn't just totally save the day*. Escorting the flag carrier in WSG? *click* -Hand of Freedom- keep killing stuff like a boss. Very useful.
Setting up Tell Me When:
TMW setup is definitely NOT intuitive. There's some good youtube guides out there, but here's a quick and dirty one for setting up inquisition. Start by typing /tmw, and right-click on any of the empty buttons to set up an icon.
Enable the icon with the checkbox and use the dropdown list to select Buff/Debuff
Typing the name of the ability in the command line. Most are preloaded into TMW and you can select it at the pane on right.
Most of the options here we don't care about, but make sure you click the Buff checkbox, and show a timer for it, and always show so it, that way it turns red and angry if you let it fall off. The icon is now set up to display, but it'll show at all times, which can get annoying, so we'll set it to only show during combat.
Click the Conditions tab at the bottom, add a condition with the green plus sign. From the dropdown menu mouseover Unit Conditions and select Unit in Combat
Move the icons wherever you want them on the screen. You'll notice there's a bazillion other options and settings for the addon, so play around with it if you want. Type /TMW again to lock everything in place. Now you're ready for a fight!
Hrm, you'll notice in that screenshot that the enemy nameplates are not default either. Yes! another mod! Threat Plates is an addon for an addon (modception? better go deeper). You'll need Tidy Plates to use Threat Plates, but both are pretty lightweight. As you see above the nameplates are big and red and have those "PAY ATTENTION TO ME" dags like store sale signs or batman "POW!" "ZIF!" "BAM!" effects. That's because I'm dps and stuff is attacking me! Now, if i were a tank, the plates would be happy and green and calm, like so:
Now the addon thinks I'm a tank, and tanks should have aggro so the plates are calm ang green, everything's right with the world. If i start to lose aggro (or gain it as DPS) the plates get bigger and yellow, then red and angry if I fully lose/gain aggro. It determines this based on the aura, or you could tell it to ignore auras and use your current spec. Good addon for DPS, absolutely AWESOME addon for tanking since you can tell at a glance exactly what mobs have your undivided attention and which need to be taunted.