The simplest way to put this is that there is no spell rotation. You simply cast whatever spell is off the cooldown, with Judgements -- primarily Judgement of Light -- as the highest priority. Crusader Strike and Divine Storm are next, followed by Consecration. It bears mentioning that Improved Judgements, which bring the cooldown of Judgement spells to 8 seconds, creates a clash between Crusader Strike and Judgements as using Crusader Strike right after a Judgement will result in them both going off the cooldown at almost the same time. You optimize your DPS by casting something while everything else is on cooldown.
If two or more spells become available at the same time -- and this will inevitably happen -- this will result in a dip in DPS. You'll want to avoid that as much as possible. Opening with a Judgement is pretty mandatory as Heart of the Crusader will benefit your next attack. You can opt to follow it with Divine Storm and then Crusader Strike to avoid early clashes, but because all the spell cooldowns are even numbers, a clash will happen anyway. The four-piece set bonus which reduces Judgement cooldowns by 1 second will lessen the clashes, but it won't remove them entirely.
You will have idle time unless you're fighting demons or undead, in which case you can insert Exorcism and Holy Wrath into the rotation. In fact, running into a fight, you can start off with Exorcism because it has a longer range than Judgements. Otherwise, you will find yourself every now and then with no more buttons to press because everything is on cooldown. You have no spammable ability like a Hunter's Steady Shot or a Shaman's Lightning Bolt, everything is an instant attack with a cooldown. For most mobs, you will have lulls between spell cooldowns where you'll rely purely on auto-attacks. It will feel like a DPS dip, but trust your Seal of Blood / of the Martyr to do its job.
Always use Avenging Wrath. Because it is now off the GCD, make a macro to use it along with a Judgement. Never use it before getting within range of a mob, as you will kill 1-2 seconds of Avenging Wrath just trying to get into position. For the most part, use it every time it's available except when you know you won't be able to reach a boss such as when Noth the Plaguebringer teleports. In cases like those, unleash it once the boss is attackable within range. This way you can maximize the 20 second uptime. If you have an on-use trinket, bind its use with Avenging Wrath. Most trinkets have a 2-minute cooldown, making it available every time wings are up. Likewise, time it to coincide with Bloodlust or Heroism.
Even against a single mob, fire off a Consecration and use Divine Storm. Even if those are AoE spells, their contribution makes up a significant chunk of our DPS. As much as possible, refrain from healing yourself with an instant Flash of Light, even when The Art of War procs. The instant heal will reset your swing timer, and it also doesn't contribute to Spiritual Attunement. [Update: the heal from an instant Flash of Light no longer resets the swing timer.]
Always stay at max range. This will matter a lot, specially against bosses with large hit boxes, like Sapphiron. Being on what seems like his side might be considered his front, so you could eat a fatal cleave. Needless to say, always attack from behind as all melee classes are supposed to do. You will sometimes find yourself attacking from the front, specially in mobile fights or during trash pulls where everything is AoE'd to kingdom come. That's fine. This is also where Expertise comes into play.
Raiding as a Retribution Paladin is easy. Doing well isn't as simple. Being a melee class, you already have some challenges to begin with. Even on the easiest raid boss in the entire game, Archavon, your DPS can dip considerably if the tank doesn't move him out of the clouds. Naxxramas is a place where you can shine because of the type of mobs in it. Most of the bosses are also undead, which should boost performance greatly. That said, even with those extra spells at your disposal, you will likely not out-DPS a similarly geared and skilled Hunter or Mage. This is why refinement of skill is mandatory. More than a fancy mace or sword, knowing how to play is going to be your best weapon in the DPS race.