Destruction is often considered to be the 'mage-like' warlock spec; this is based on its more dwarven style of play (fight, drink, fight, drink...). It is true that destruction relies more on direct damage than DoTs or the damage done by minions, but don't be fooled, destro locks are not just emo-mages.
Where the other lock specs focus on shadow magic, destruction primarily makes use of fire spells. Incinerate takes the place of Shadow Bolt as a filler, and Conflagrate and Chaos Bolt are added to the spell book making a dazzling array of... well, destruction.
Destruction locks have the greatest 'burst' potential. This means that they can deliver a high level of DPS very quickly. This makes them ideal for short fights and swapping between multiple targets.
Destro locks are also very mana efficient -- not because they don't get through their mana (they certainly do!) but because they have so much mana restored through Improved Soul Leech.
While destro has a lot of burst it doesn't have an execute phase. With such a flat DPS distribution it can be hard to make the most of DPS boosting effects such as potions, trinkets and Bloodlust or Heroism.
Since you can't get your hands on ISL until level 45 at the earliest, you can find yourself having to regenerate mana between fights a lot. Don't forget that you don't have to rely on just drinking for this, you can speed things up by tapping and then either eating and drinking at the same time or bandaging (or using Cannibalize, if you're Forsaken).
Stats to look for
As with demonology, the destruction talent tree doesn't offer any hit rating. This does mean that you need to dip into affliction to beef this up to the cap if your gear is lacking but generally it's worth trying to attain cap from gear alone.
Once you have the hit cap then spell power is by far the best stat to go for. Spirit, haste and crit are all good but not as good as a nice stack of spell power. If you want to get stat weighting values for your gear level then SimulationCraft can help there, check out the Blood Pact guide on how to use it if you've not done so before.
Stats to avoid
As with all warlock builds, you don't need melee or regeneration stats. Intellect and stamina will increase sufficiently as your gear level increases so don't seek them out either.
Leveling as destruction
Leveling as demo can be great fun. You still have the option of getting your minion to hold onto things while you blow them (or their friend) up but as you progress you will probably want to just use the imp and blast things as quickly as you can.
Beyond the normal talents, those I find useful specifically for leveling are:
- Shadowburn - The warlock equivalent of a shotgun. To quote Hicks "I like to keep this handy... for close encounters"
- Destructive Reach - The more time they have to spend running towards you, the less time they spend beating on you.
- Shadowfury - This spell is just too much fun not to play with.
Your basic destruction rotation
Your basic raiding rotation for destruction is by far the simplest of the three trees. Keep Immolate and a curse on the target, keep Conflagrate and Chaos Bolt on cooldown, fill with Incinerate -- that's about it.
You can see a flow of the spell priorities in the chart to the right. This doesn't include Life Tap but you only need to cast that if you get low on mana -- since you aren't activating a glyph buff. If you have to move and don't have a Conflagrate or curse to cast then it's worth tapping to save having to do it later.
Curse of Agony will actually deliver more DPS than Curse of Doom but because it will need more casting your overall DPS will drop, so only use it within the last minute or so of the fight.
You can include Corruption into your rotation but this is a slight DPS drop on a standard fight and adds more complexity in that you have more spells to cast. Not only does this add Corruption casts you will probably need to tap more as the Improved Corruption talent is typically paid for by dropping Soul Leech.
Over the page for a look at talents and enhancements.