On most cata realms, destruction is considered as a "bad" spec, no one wants to play it, no one dares try it. This has lasted long enough, since there's no destro guide in PvP I decided to write one myself.
Note that what I say is not absolute truth, if you think I'm wrong about some points please tell me. Just don't be disrespectful if you do so. (same for spelling or grammar mistakes)
I might edit this to add some parts.


I Introduction
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Destro is an interesting spec, it offers lots of possibilities. It may be difficult to play, yet not as difficult as it's said. The main goal of a destrolock is to get the control of everything as soon as possible, then keep it and wait for an opportunity to burn them down. I don't know any spec that's played like destro, if you don't know it yet you may love it, you may hate it, but you should try it.
I won't talk about things like reforge, gems, items, spell rotation or things like that here (or at least no yet). It's boring, if you want them PvE guides are better. Le's focus on gameplay.

II Main spells, how to use them
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Immolate
Our most important spell, it does most of the DPS and allows to cast Conflagrate. If you don't have it on your target, your main goal is to cast it. The problem is that it's not instant, it have to be casted. Usually Shadowfury allows to cast it safely, if it fails just use death coil. Of course don't ever lose it, keep it up with Fel Flames.

Fel flame
This instant spell allows to keep Immolate up without having to cast it. If Immolate duration is below 50% left, think about when and how you will cast a fel flame. If it's below 25%, forget everything else and cast it.
Remember, it takes some time to reach the target, Immolate can end before the flame hits your target.

Shadowfury
instant, 3s stun, AoE. It has a short CD, so you can use it often. Its main use is to safely cast Immolate, or spells like Fear if you already have Immo. In AoE situations like a big BG fight, try to follow it with a Howl of terror. It doesn't share DR with any other lock cc.
Careful thought, it's a stun. A DK with the ice thing CD is immune, and a mage will probably blink to break it and cs your immo/fear.

Death coil
Instant, 3 or 3.5s cc, doesn't share DR. It can be used to cast Immo if the Shadowfury was broken. Basically use it when you need a Shadowfury but it's on CD.
Note that it takes some time to reach the target. That means it's bad to break a cast, but it's excellent when you know you're about to get cc'ed, your cc will be delayed.

Conflagrate
Instant, high damage, slow, low CD, this spell is perfect. Against melee it should be timed with Shadowflame to keep a slow effect. Against everything else cast it as soon as you can, unless you have to cast a Fel flame of course.
It deals 60% of Immo damage. That means the more haste you got, the harder it'll hit. And don't forget DoT snapshoting actually works with haste procs / BL...

Fear
Powerful cc, but not instant. It's used when you need some time to cast dots, curses, and why not follow by a hardacted Soulfire.
Be careful, don't ever overestimate this spell. Most class can and will break it. If you run out of instant cc before you get an Immo because you thought a Fear was better, you're dead.

Curses
We have 3 curses : Elements, Tongues, and Weakness. Don't forget them, they are really powerful, and since they are instant they are easy to use.
Use Elements ONLY when there are several casters on your target, or when other curses are useless (enh shaman). If you're the only caster, always use Tongues against another caster, and Weakness against a melee.

Incinerate
Our free cast spell. Don't forget we're not doing PvE, we actually hardly ever use it. Cast it only when you really have nothing better to do, and when no one focus you.

Chaos bolt
It's used more or less in the same situation as Incinerate, but it has some interesting uses. It can damage a hunter with Deterrence or a rogue with a Cloak, even if it still gets reduced from Deterrence. It can also finish a pal or priest that used an absorb effect just before they get killed.

Demonic circle
This is a really powerful spell, but not easy to use. When you have time to place it (duel, defending) always place it out of LoS. It will allow to break enemy cast, and get out of a melee's range without risking a charge. Careful though, getting out of LoS when you're low health is dangerous, you can't be healed.
When you start a random fight at the middle of a BG, place it as soon as you go down of your mount. Try to get away from it when you cast instant spells.
When facing classes like rogue, DK or war, keep it for the moment when they're immuned to your cc. Against other melee classes, just use it when you get at melee range, like you would use a disengage. Against a caster, try to place yourself so that your target / focus is between you and the portal, and tp when you need to break a cast. This doesn't work against all spells.

Armors
Actually, we don't have only Fel armor, we also have the Demon one. Everyone will tell you to use Fel and forget Demon, but actually both are excellent. Fel increases your damage and heals you by 6% of your damages, but Demon increased healing received by 30%. Tha't huge. As soon as you get focused and if there's a healer not too far, don't ask questions and cast Demon. It also increases healing from Healthstone.

Shadowflame
When glyphed, it slows by 70%. Against a melee you should get close to your target to cast it when Conflagrate ends, the slow is so important you'll easily get away after it.
Note that it's a PHYSICAL effect. That means it can only be dispelled by effects that specifically remove slows, and more important, it works on DK with anti magic shield.

Nether ward / protection
Absorbs magical damages, and protects you from that spell school. I don't know if it's a bug, but the damage reduction only works when the ward isn't broken on first hit. It makes the spell specially powerful when you have DoTs on you, before you receive a big damage spell of the same school (like the shaman lava burst on flame shock).

Soulburn
Usually it's used to cast a free Soulfire at the beginning of a burst, to get the damage buff. On long fights, keep it to get an instant casted pet summon, when needed.

Healthstone
It's not really powerful, but still free heal, if you die without using a stone you did something wrong. For extra effect use it with Demon armor.


III Pets
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Felhunter
It's the pet most destrolocks use. It has one of the few things that destrolock lacks : a way to punish hardcasted spells. Try to use the silence if you ever lose control against a caster.
It also have an offensive magic dispel. On short fights use it when there's something interesting to dispel, like a proc or a burst effect. On long fights use it as soon as possible until there's no more buff.

Succubus
The other popular pet. I don't really like it, since Seduction is slow and shares DR with fear. The bump can be OP, but in very specific situations. On a flat ground, it doesn't bump target very far.

Imp
Probably not the best, but my favourite. The 6s cd defensive magic dispel is AWESOME. It can be casted when you're cc'ed. And most cc are magic. It means that against some classes like pal, it a 6s cd pvp trinket. Yeah, that's OP. It can also remove mage deep freeze or combustion, all silences except the rogue opener, dispels DoTs... Just be careful, don't dispel a sham fire shock, unless you really know what you're doing.
With right talents it also grants random free Soulfire.
Don't chose this pet if you want to play in a serious way, but if you want to have fun it's the way to go. If you already play destro and get bored, give it a try.

Voidwalker
Don't use this pet. It has two uses : the bubble, and the stealth detection. The bubble is viable only when casted before the summoning of another pet before a duel, but that's not fair since it only works in duel. The stealth detection is extremely powerful, but the rogue will jump on you as soon as you finish the summoning, and with this pet against a rogue... You're dead.



IV Talens
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There are a lot of possibilities, I change my talents so often there's no point in copying mine. I used a color code on this picture : take the green talents without question, the yellow ones are the other good ones, and the red ones the talents you should use only if you play with the Imp. Avoid talents without color.

You could use the talents I used when I made the screen, but I would not advice it for beginners, and it's an Imp spec.
You may ask why I put Demonic rebirth in green. It's because at least on Neltharion, everyone always focus the pet. I've never understood why they think killing a lock pet is useful, but if it pleases them... Anyway, it makes this talent something you must have.


V Glyphs
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Prime :
Immolate : up the damage of both Immolate and Conflagrate, two of our main damage sources.
Shadowburn : Double execute + double soul leech regen, awesome in close fight.
Conflagrate : More instant damage, more slow

Major :
Shadowflame : take it without question, I can't imagine a destrolock in PvP without this glyph. Allow to always slow a melee, and 70%... Not all classes have a slow that powerful.
Death coil : It depends on your haste. Try to cast a fear after a death coil, if it ends before the cast get the glyph. Try it at melee range.
Demonic circle : if you can't get far from melee, this will help.
Soul link : Better resistance, a destrolock usually gets focused a lot.
Other good glyphs : Healthstone for even more regen, Soulstone if you usually bg with a healer, howl of terror because it's fun in BG.


Minor :
Unending breath is the only one kind of useful here.



VI macros
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Usually I don't give macros, they are something personal. But there are some macros that are always useful :

Code:
/petmoveto
This one allow to move the pet wherever you want to. Useful when you don't want it to be hit by AoE cc.

Code:
/cast soulburn
/cast soulfire
Instant soulfire. Of course you should bind this macro, soulburn and soulfire on different keys, not just the macro.

Code:
/castsequence Fel armor, Demon armor
Armor switch.

Code:
/cast [pet:Imp,help][pet:Imp,@player] singe magic
/cast [pet:felhunter] Devour magic
A macro that casts different spell for each pet, and allow to bind pet spells, and casts imp dispel on you when you have an hostile target.



VII Random tips
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Duel, duel a lot, duel until you kill everyone. If you lose against someone, spam /duel until he's dead. Once everyone is dead, remove some gear and repeat.
However at least on Neltharion most people in dueling zone are *******s, they will insult you if you win and if you lose, try to ignore them. You must duel to get better.

keybinds. No matter what addons you have, how long you play or anything like that, keybind IS better than clicking your spells. If you're too lazy to keybind everything, at least do it for shadowfury. Clicking that spell should be punished by death.

Don't use spells that are not instant, unless everyone why focus you is cc'ed. Instant spells are enough to kill most non-healer spec. It's not something you must do, but it's a good thing to be used to it.

Don't wait too long to pup your burst : as soon as you have your dots, some instant high damage spells up, and an instant cc in case he tries to defend himself, burn your target.

Remember, dot snapshotting works with haste. That means your dots will keep the haste you had the moment you casted it. And more immo ticks means bigger conflagrate. And you can keep a buffed immo forever with fel flame. Imagine all the possibilities with things like BL, PvE trinkets, herblism thing...

If you have a hard time against a war, their charge have a minimal range. Stay close enough and they won't harm you.

Look at this link, there are a lot of useful infos here. Some are already on this guide, but not all of them.



VIII Videos