That's quite a number of things to watch out for, so I recommend keeping and configuring an addon to help you keep track of everything at first. Don't sweat it too much if you sometimes cast a lower-priority spell before a higher-priority one; a spell priority list can be forgiving and you don't have a reliance on DoT uptime the way affliction warlocks do. Keep in mind that the Cremation talent enables Hand of Gul'dan to refresh Immolation on the target, so optimize your DPS by casting Hand of Gul'dan instead of Immolate when appropriate (i.e., just before Immolate expires). I should also mention that if you're within range, you should pop Immolation Aura when in demon form because it deals sweet damage. Cast Shadowflame because of its significantly improved damage. These are both on low priority, because few fights allow you to actually be (safely) in range to cast either spell.
You should be glyphed with Glyph of Immolate (prime), Glyph of Incinerate (prime) and Glyph of Metamorphosis (prime). You can opt to replace the Glyph of Incinerate with Glyph of Felguard (prime), which increases your felguard's Legion Strike damage by 5 percent, but the numbers will tip in Incinerate's favor because of accompanying effects that increase its damage. You have a lot of flexibility when it comes to major glyphs, seeing as how none of them contribute directly to your key DPS spells, so beyond Glyph of Life Tap (major) and Glyph of Shadow Bolt (major), which only contribute to efficiency, pop in whatever strikes your fancy. Glyph of Demonic Circle (major) will probably be the most useful, especially in mobility fights.
In case you haven't allocated your talent points yet, take a look at this talent spec for demonology. Note that Demonic Empowerment doesn't confer any straight DPS increase but is a pure utility spell that's probably more useful in PvP. If you don't think you'll be using Demonic Empowerment (your felguard isn't likely to encounter much crowd control in PvE), feel free to swap that point elsewhere such as Aura of Foreboding to keep targets in place.
Destruction One of the biggest things with destruction is the massive nerf to Searing Pain, making it absolutely worthless to the spec (or any non-PvP warlock, for that matter). Don't look to be using Searing Pain after the nerf, although the spell was aces for a short while after 4.0.1 went live. I have to point out that this rebalance to the spell is to prevent it from being ridiculous at level 80, and it should probably be usable again at level 85. Unlike affliction warlocks, whose optimal pet has changed, you're still best off using your ever-reliable (albeit whiny) imp.
Your spell priority list should run through Immolate, Conglagrate, Bane of Doom, Shadowflame, Corruption, Chaos Bolt and Incinerate. On top of everything, you should open with Soul Fire to apply the Improved Soul Fire effect and maintain it as long as your target stays above 80 percent health. You should also cast Soul Fire whenever Empowered Imp procs. Overall, not too much to watch out for, but with the number of things on your plate, you'll always be casting something, which means haste is your friend after getting hit-capped and stocking up on spellpower through intellect. Shadowflame is excellent for destruction warlocks, so use it whenever you can get in range.
Your best glyphs for destruction are Glyph of Conflagrate (prime), Glyph of Immolate (prime) and Glyph of Imp (prime). Consider swapping Glyph of Incinerate for Glyph of Imp; although Incinerate is pretty low on your spell priority list, the DPS spread between the two gifts will be marginal. I'm partial to the Glyph of Chaos Bolt (prime), but from all reports, the glyph doesn't appear to be a significant increase in DPS compared to either glyph. You have even more freedom with major glyphs than either of the other two specs because you won't even be casting Shadow Bolt, so the only glyph that's reasonably usable would be Glyph of Life Tap (major) to reduce your downtime when you tap for mana.
Check this talent spec for destruction PvE, with a special note to the utility spell Bane of Havoc. While not necessarily something you'd use in a regular DPS rotation, the talent's situational use is stellar. Think of it as a reverse Beacon of Light. In situations where you'll need to split your attention, you can apply Bane of Havoc on one target while switching to DPS another, such as boss fights where adds enter the fray. It will be in the use of abilities like this that good warlocks will be able to distinguish themselves from mediocre ones. Destruction warlocks should also take advantage of Shadowburn, which works as a means to replenish Soul Shards while in combat, although its low damage and short window for use makes it less than ideal for most DPS rotations.
Don't fret over the new mechanic so much. It's a great upgrade to the class playstyle, but for most players, it'll be an impalpable change aside from the additional bag space. The important thing to remember is that some of these rotations and numbers will change when players hit level 85. Abilities such as Demon Soul will make numbers jump significantly and hopefully push back felhunters back into the fore for affliction warlocks. Fel Flame will work itself into rotations, changing up things depending on its actual damage. Everything from here until Dec. 7 is temporary -- a transitional phase -- so don't worry too much if you're not topping the meters like you're used to. For now, it's important to get a feel for the new talents, an understanding of the mastery spec, and figure out what spec you'd like to play in the upcoming endgame.
Blood Pact is a weekly column detailing DoTs, demons and all the dastardly deeds done by warlocks. We'll steer you toward tip-top trinkets and Soulburning your way through Cataclysm.