Shaman Leveling Guide (Level 1-30) - Talents, Rotations, Races & More

Weapon: Any 2h'er with as much damage as humanly possible. Once you get Stormstrike you want the slowest weapon possible, but until then the speed isn't particularly relevant. If you're tanking you definitely want to use a shield and any good 1h'er you can find, otherwise I wouldn't use a shield imo.
BiS at level 20 is either Forsaken Greataxe from a Ruins of Lordaeron quest or Hammerbone from Leaders of the Fang quest in WC - for alliance you want Smite's Mighty Hammer from Deadmines

Gearing
Whatever will net you the highest AP is typically best, but almost all stats are good for enhance.
Strength is our best stat as it gives 2 ap per point
Intellect is probably second best since it provides 1 ap per point, spell crit, and increases your total mana pool
Agility is obviously good, it gives you crit for both attacks and spells, but per point it's a bit less efficient
Spirit isn't useless as it improves your mp5 but I wouldn't make many gearing decisions around it unless you lose like 1 pt of something else and gain 5+ spirit or something
Spell Power is unfortunately quite weak since the spell power scaling for Shaman spells is legitimately 1/5 as potent as it is for other classes, blizzard will likely change this but as it stands spell power is insanely inefficient.

Consumables: (at level 20)
Longjaw Mud Snapper Food for 10 ap & 5% EXP bonus
Elixir of Ogre Strength for 8 str
Elixir of Lesser Agility for 8 agi
Elixir of Firepower for 10 fire spell damage
Elixir of Wisdom for 6 int
Heavy Sharpening stone & Heavy Weightstone for +4 weapon damage

Mana Well for mp5 (Alchemy) > Lodestone melee AP (mining) > Fish Bowl 8% Stats (fishing) > Sharpening Wheel strength (blacksmithing) > Chair 2% crit (skinning)

Tent from leatherworking I would use on CD since it gives 5% rested xp

Mana efficiency is crucial for uptime while going from mob to mob. To maximize uptime you want to take advantage of the mp5 rule, where 5s after not casting a mana consuming spell you start your mana regeneration. Ideally you want to frontload your spellcasts upon pulling a mob so the majority of the time fighting you are regenerating mana. Follow the prio list, then just afk meleeing the mob until it's dead. If you want more total damage at the cost of mana efficiency, just smash all your buttons following the priority list

Obviously keep up Flametongue Weapon or Rockbiter Weapon permanently. After a bit of testing it's indistinguishable to me which is better at this level range, however Rockbiter Weapon makes your tanks life miserable so I opt for Flametongue Weapon, and some mobs are resistant/immune to fire damage so keep that in mind

Solo Open World Rotation 10-20
1) Lightning Shield pre-pull
2) Flame Shock to pull the mob - you can save your shock CD if the mob is a caster with a dangerous cast that you'd rather Earth Shock
3) Drop Searing Totem
4) Fire Nova if there are more than 2 targets, or you need the damage immediately
5) Earth Shock on CD to kick or use for damage (if the target is already debuffed with Flame Shock or is going to die soon)

Dungeon Rotation: 10-20
When there are multiple targets, especially 3+ Fire Nova is one of the best spells in the entire game, however it is rather mana intensive. If your mana recovery is low and you don't have much time to drink, you ideally pretty much only want to spend mana on Fire Nova because it is so damage efficient. If you have extra mana to play with, use it at your discretion
1) Flame Shock
2) Searing Totem
3) Fire Nova on CD
4) AFK and auto attack for MP5
5) Earth Shock if there is a cast that needs to be kicked aka Fear or Healing Touch etc

Strength of Earth Totem is pretty weak at low levels, however it doesn't cost much mana and it has a 30 yard range, so it's not a bad idea to pre-place it if you're in an area where you know you'll fight multiple packs of monsters, or a boss. Otherwise I don't think it's worth the mana dropping it every single pull.

Utility:
Earthbind Totem & Frost Shock are great for kiting/slowing mobs or enemy players
Stoneclaw Totem is great if you pull too many mobs and need a bit more defense or an opportunity to heal
Tremor Totem is great to cleanse fear/sleep/charm effects. It ticks every 4s so if you anticipate yourself being feared drop it accordingly. Conversely if you see a teammate about to get feared, don't drop the totem pre-emptively as it ticks the moment you drop it, so it won't tick again for another 4s. Instead, wait for the fear cast to go off and make sure to not global lock yourself, and immediately drop it then to cleanse it instantly
Stoneskin Totem is alright if your tank is a whimp or you need some DR fighting harder mobs
Cure Poison is great when fighting mobs that poison you obviously
Purge is great for griefing enemy players removing their buffs, or powerful buffs on npcs such as healing effects