Attribute Enhancement

Spell power:

A very important attribute in spell school that increases the damage done with spells. As for a warlock, Bonus damage is increased by Empowered Corruption.

Stamina:

Increased stamina not only provides extra health but also means life tap can be used more. This attribute is supported by talent Demonic Embrace which provides extra bonus to both a warlock and the pet's stamina per talent.

Intellect:

Increases Maximum mana points and slightly increase Crit Chance. With talent support, your demon pet's intellect can also be increased along with yours.

Spirit:

Becomes apparently useful In WlK. Increased Spirit provides the bonus damage of your Fel armor.

Spell hit rating & Spell crit chance:

All Warlock abilities are supported by Spell hit rating. Choosing DOT as main damage output indicates you need to attach greater importance to HR than Crit. However, if you choose Destruction and use mainly shadowbolt, these attributes are of equal value then.

Haste Rating:

A nice attribute, high haste rating shortened the global cooldown value of 1.5 seconds to much extend especially when you are a non- Demonology warlock. Demonology warlocks benefit very little from Haste Rating.

Summary:

Unlike other casters that requires high on mana, warlock is a standard caster as DPS with support of life tap ability. For a warlock, spell hit rating is in the first place, Spell crit chance, spell power and Haste Rating comes after. As for the basic attributes, while Stamina is preferred when solo, players still value spirit more in RAID. Among 3 attributes, intellect is less important because of the MP/5 basis.