The stat priority for an Enhancement Shaman is:
Agility;
Hit Rating and Expertise Rating (until 7.5% caps);
Mastery Rating;
Haste Rating and Critical Strike Rating.
Agility provides you with Attack Power, which increases the damage if your melee attacks, and Spell Power (through Mental Quickness), which increases the damage of your spells. Agility also increases your critical strike chance.
Hit Rating decreases the chance that your melee attacks will miss their target (7.5% against a raid boss). Therefore, your goal is to reach the 7.5% hit cap (see section below), which will ensure that your attacks never miss.
If you are dual-wielding, reaching the 7.5% hit cap will only prevent your special melee attacks (yellow attacks) from missing. Your normal melee attacks (white attacks) will still miss because, when dual-wielding, they have a 26.5% chance to miss by default. Even in this case, it is unnecessary to keep stacking Hit Rating after the 7.5% hit cap.
Expertise Rating decreases the chance that your melee attacks will be dodged (7.5% against a raid boss). Therefore, your goal is to reach the 7.5% expertise cap (see section below), which will ensure that your attacks are never dodged. Note that you should always be attacking bosses from behind, which prevents them from parrying your attacks. Therefore, it is usually unnecessary (unless the boss cannot be attacked from behind) to decrease the chance that your attacks will be parried (something that you can do by stacking Expertise Rating after reaching the 7.5% cap).
Note that both Hit Rating and Expertise Rating reduce your chance to miss with spells, which is 15% against raid bosses. This means that when you reach the 7.5% melee hit cap and the 7.5% expertise cap, you also reach the 15% spell hit cap.
Mastery Rating, through Mastery: Enhanced Elements, increases the damage you do with spells, which make up for a large portion of your damage.
Haste Rating increases the speed of your melee autoattacks, enabling you to get more uptime on Windfury Weapon.
Critical Strike Rating increases the damage of your attacks and spells, and grants you more uptime on Flurry.
Hit Cap
At level 90, most races require 2,550 Hit Rating to reach the melee hit cap. Draenei, thanks to Heroic Presence, only need 2,210 Hit Rating.
Expertise Cap
At level 90, most races require 2,550 Expertise Rating to reach the expertise cap. Some races, in some cases, only need 2,210 Expertise Rating, thanks to passive racial skills:
Dwarves when dual-wielding Maces ( Mace Specialization);
Orcs when dual-wielding Axes ( Axe Specialization).
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MACROS:
*Trash mobs- Single/AOE:
#showtooltip
/startattack
/castsequence reset=5 Flame Shock, Lava Lash, Stormstrike, Unleash Elements, Elemental Blast
/use !Fire Nova
/cast Shamanistic Rage
(Note: Elemental Blast=Talent and be sure to use Lightning Bolt when Maelstrom Weapon Occurs for single targets and Chain Lightning for multiple targets)
*BOSS:
#showtooltip
/startattack
/castsequence reset=7 Flame Shock, Lava Lash, Stormstrike, Unleash Elements, Earth Shock, Lava Lash, Stormstrike
/use !Fire Nova
/cast Shamanistic Rage
