During 4.0.1 we all got used to a nice and simple rotation using almost every available GCD if Haste-capped. Now that the haste-cap is pretty much unattainable there's plenty of dead space, throwing timings off and leading to more cooldown watching, rather than less. To address this third-party add-ons are configured specifically to reduce the information overload during encounters, CLCInfo (previously CLCRet) being a prime example targeted at Retribution's Rotation, but you shouldn't use them as an excuse to disconnect the brain entirely.
One of the weaknesses of the current Retribution Rotation that can cause players to have a brain fart is Inquisition, more specifically when to recast Inquisition. If Holy Power generation was nice and smooth and regular the answer would be pretty trivial, but throwing in the proc mechanics of Divine Purpose and Hand of Light can sometimes throw you for a loop. Because of this, and the strange interaction 4 pc Tier 11 has with the rotation, it's best not to let an add-on do the thinking for you.
The basic rotation/priority system for level 85 Retribution DPS is:
Inquisition > Hammer of Wrath > Exorcism > Templar's Verdict > Crusader Strike > Judgement > Holy Wrath > Consecration
Fairly obviously Inquisition should be up pretty much 100% of the time (expect for periods when you're not DPSing), and it's easier in the basic case to rebuff for a full 30 second duration. Assuming a 3 Holy Power Inquisition is optimal, the longer that buff is up without being re-cast the more resource efficient it is (Both in terms of Holy Power and GCD's used). Unsurprisingly re-casting Inquisition as late as possible requires a certain amount of pre-planning - you don't suddenly have 3 Holy Power to use just because you need it!
Laying out the maths is a little over the top, but it works out that you're okay continuing to spend Holy Power on TV whilst you have more than 6 seconds left on Inquisition. Less than 6 seconds left should mean that you re-cast Inquisition as soon as have 3 Holy Power or a proc of Hand of Light.
The only other important consideration is that first cast of Inquisition upon engaging a boss or if you've allowed the buff to fall off and have zero Holy Power. In these cases it's more important to get the buff up with a solid duration of 20 seconds rather than wait for 3 Holy Power.
The time sensitive nature of Inquisition reinforces the need for an Add-on that tracks the buffs duration and displays it conveniently. I use CLCInfo for the purpose mainly because it was handy at the time I was re-learning 4.0 keybinds and tinkering with my UI, but any number of tools like Power Auras, ForteXorcist, ClassTimers and IceHud for RealUI would do the job just as well. Perhaps better in fact as they're designed for that sort of functionality.
Special Case- Sapphirium Battleplate 4 Piece Bonus
Once you've gathered four parts of your Tier 11 your Inquisitions will last for an additional 10 seconds. You might think that this is license to use 3 Holy Power and only cast it once every 40 seconds, but it's not quite that simple.
Inquisition also procs Divine Purpose, with the same frequency no matter the amount of Holy Power used. This means that casting Inquisition using less Holy Power is more efficient from a HP resource perspective -
Without 4-Piece, 40% Chance of Holy Power via Divine Purpose Proc per Cast
10s Duration - 1 HP Cost - 0.06 HP per second
20s Duration - 2 HP Cost - 0.08 HP per second
30s Duration - 3 HP Cost - 0.10 HP per second
20s Duration - 1 HP Cost - 0.05 HP per second
30s Duration - 2 HP Cost - 0.067 HP per second
40s Duration - 3 HP Cost - 0.075 HP per second
We tend to cast Inquisition every 25-30 seconds because it has the lowest GCD cost. Casting every 15-20 seconds would start to interfere with the cooldown of other abilities especially when Art of War is factored in, and that flexibility is important. With 4 Piece Tier 11 we can make use of this more optimum usage of GCD's but make it 33% more cost-effective under ideal conditions. Subject to the vagaries of an encounter, refreshing Inquisition with 2 Holy Power for 30 second duration is usually better than 3HP for 40 whilst still adhering to the rule of looking to rebuff when the duration is < 6 seconds. Of additional non-trivial consideration is that 2HP Inquisitions are far easier to cast - it'll take at worst 2 Crusader Strikes to generate the resources you need, rather than 3.
Remember than none of the above are hard and fast "Laws of Good DPS" to adhere to come hell or high water, I just want to express how key being aware of your timings can be even with something as simple as keeping a buff up. Encounter mechanics will play havoc with your rotation at the best of times, so having a few simple guidelines to follow should help you to concentrate on the encounter more than rotation.
It's been stated that Divine Purpose is likely to change in the future, probably eliminating the additional Holy Power proc in favour of moving the Hand of Light Mastery effect into the tree in this position. If mechanics are changed in this fashion you'll be using every Hand of Light Proc on Templar's Verdict and alternating Inquisition with TV as you max out your Holy Power bar. We'll see how the changes play out when they're announced in detail.