It's a matter of luck
The first thing that you must always keep in mind when selecting which item to get first using your valor points is the small matter of the item that it would be replacing. Very few people are going to have the exact same gearing, even if they play the same spec in the same guild. Drop RNG can completely change which items you use and which you just can't quite give up yet.
Always upgrade from the lowest ilevel piece first, if you can manage it. Doing this is always going to provide you with the largest overall stat gain in the vast majority of situations, which is always worth it. For most warlocks, this is probably going to be the wand slot. Wands were beyond difficult to get in the last raiding tier, particularly for DPS casters who weren't able to use spirit. While ZA/ZG came out with a nice wand as a substitute, it still was not quite the same as a raiding-quality wand.
After that, your next weakest point is probably going to be one of your ring slots, depending on the level of raiding that you were in before heading into Firelands (with a little bit of luck tossed in). Even if your ring is one of the weaker slots, that is one that I wouldn't really suggest switching off early.
Ilevel is a large factor when choosing which pieces to upgrade first, but it isn't the only factor. The wand is more than likely your best shot simply because it is more than likely going to be far lower than the rest of your gear, but rings may or may not be; most of them may even be on par with your gear.
How to properly juggle hit
Which makes or breaks the case of the ring is how badly you need the hit. Sure, sure, hit is such a trivial stat to have or not have on gear nowadays because we can just choose to reforge whatever stat we don't want into hit and be done with it. ... Totally wrong. Well, okay, it isn't totally wrong -- it is actually right -- but this principle is a doubled-edged sword.
Every spec has its favorite secondary stat, whatever it may be, and hit is always right up there on the list until the cap. In some cases, it may not end up being the best secondary stat, but it is always strong. This means that you always want to have hit alongside your best secondary stat.
Say you favor haste. Let's also so that crit is your worst secondary stat. If an item has haste/crit on it, then it's perfect. Ideally, you would want to get a haste/hit item, so whether you reforge crit off of one or completely replace it via the other doesn't matter. The end result is the same.
The problem comes when you have suboptimal items. Now, the item in question is mastery/crit, which is only so-so for you, but you still need the hit. You would still want to reforge the crit into hit -- but you aren't just giving up crit for hit anymore; you are also giving up mastery for haste. Now, were that a mastery/hit item, you would still have to give up some haste, but you could reforge some of the mastery and get a portion of it back. See?
In an optimal setting, it doesn't matter if you use hit gear or non-hit gear in order to reach the hit cap. In a nonoptimal setting, you want to push for the hit gear as much as possible.
Back to those rings
Why bring this up? This is what will determine whether or not you get the ring first.
Let's face it: All DPS casters still need some hit gear. We've done what we had to do in order to reach the cap, but getting actual, real hit items would be stellar. Right now, unless you happen to be wearing the Soul-Blaze Robes from Nefarian, you won't really have hit on either your chest or your rings. It is possible that Nezir was kind to you and did drop a ring with hit on it, but barring that, there isn't a way to have hit on either of these slots.
Why does that matter? Because it determines which you should get next. Both the new tier chest and the ring are hit items. The chest is haste/hit, which most people really want, while the ring is mastery/hit, which is still top-shelf even if it isn't the best. If you currently have hit from either a ring or your chest and you are reforging any piece that doesn't have your most optimal secondary stat on it for hit, then you go for one of the hit items first.
Using the old tier chest? Get the new chest first.
Neither of your rings have hit on them and you are using the Nef chest? Get the ring first.
Neither of your rings have hit and you are using the old tier chest? Favor the chest first.
Why not rush for tier gear?
The most common thing that I see people do in situation such as this is that they always, always rush off for their tier gear first. The simple matter is this: Everything is an upgrade. You want it all eventually. Get the upgrades that you can get now first, and get the ones that come later, later. The old four-piece set bonus is rather lame; people want to get the new one, but think before you spend. Tier gear generally isn't more of an upgrade than any other item. The only exception is when you break a weak set bonus for a strong set bonus.
First, you really don't want to get your tier gloves, anyway. They can be nice in some situations, but Ragnaros drops a wicked-awesome pair of cloth gloves that are far better than your tier piece. Spending valor points on your tier gloves isn't the wisest choice if you want use them for an extended period of time.
Second, Baradin Hold has a chance of dropping your legs. Unless you already got the gloves to drop, there's very little chance that buying the legs is going to instantly get your four-piece bonus. Remember, we aren't planning on buying the gloves, so that means you need to get the pieces from Staghelm and Ragnaros first. Even if you do buy the gloves, you still need one of those other pieces.
Third, it's all a matter of itemization. Reforging fixes a lot of the itemization "issue," but it doesn't fully remove it. Say you play affliction. An item with haste/mastery on it is going to hold more weight than an item with crit/mastery on it, even after you reforge the crit into haste. You only manage to salvage some of the item, not the entire thing. Intellect levels make a difference, but whether or not that saves you really depends on what ilevels you are changing from.
Your final game plan
I know a talked a bit about the philosophy behind the choices that you should make, but that's because nothing is all that cut and dry. Anyone who ever tells you, "This is the itemization path you need to follow without question" is lying to you. What you should get next is always determined by what you have now. Here's how it should go.
Wand, if using ZA or lesser wand or in full heroic gear
Ring, if reforging non-haste gear to hit
Tier chest, if not reforging non-haste gear to hit
Tier legs, if you have three other tier pieces
Wand, if using BOE drop but not in heroic gear
Ring, if not reforging non-haste gear to hit
Wrists, if not using an alt to farm valor
Tier gloves, if you have three other pieces
Necklace, assuming RNG hates you
Isn't that just fun? It's like the old feral druid rotation, only with gearing! Seriously, though, it isn't that bad -- and the truth is that you can honestly spend your valor points however you want and it won't make much of a difference either way. Have fun, kiddies!
Blood Pact is a weekly column detailing DoTs, demons and all the dastardly deeds done by warlocks. We'll coach you in the fine art of staying alive, help pick the best target for Dark Intent, and steer you through encounters such as Blackwing Descent and The Bastion of Twilight.