Basic Mechanics of Arcane
Arcane Mages primarily work on two principles; the use of the Arcane Blast spell to rapidly increase your damage and the conservation of mana to maximise the damage of each spell cast. Each time you cast Arcane Blast you gain an Arcane Blast buff stack. This buff stacks up to four times and as they add up the amount of damage your Arcane Blast spell does increases, but so does the mana cost of the Arcane Blast spell. However, the Arcane mastery bonus increases damage based on total mana you have remaining in your mana pool. As you may well have guessed, these two principles do not go well together. Your task is to make these principles fit together as best as you can.
Thankfully you can clear Arcane Blast stacks by cast any Arcane damage spell except Arcane Blast or Arcane Explosion, so although you lose the stacked damage bonus you are resetting the mana cost back to its base level. You will usually seek to clear Arcane Blast stacks with Arcane Missiles. This spell costs no mana, but can only be cast when it 'procs'. Arcane missiles has a chance to proc on any offensive spell cast. The third spell you will come across is Arcane Barrage, this is far less effective as it costs mana and has a cooldown period therefore it should only be used in a last resort if Arcane Missiles has not proc'd.
You will always do more damage by continually casting Arcane Blast with 4 stacks of the spell buff than conserving mana for the mastery bonus by clearing stacks. However, if you continually cast Arcane Blast without clearing stacks you will run out of mana very very quickly and therefore be useless. Therefore you must utilise mana restoring abilities to allow you periods where you can continually cast Arcane Blast (called burn phases) and maintain a relatively mana neutral casting rotation when your mana regeneration abilities are on cooldown (called the conservation or conserve phase). These are the simple mechanics that form the basis of the Arcane Mage rotation.
Mastery; How It Works
Mana Adept: This increases all spell damage by a certain percentage based on your Mage's mastery score and the amount of mana remaining in the mana pool when the spell is cast.
Initially your mastery bonus if 12%, although this will increase as you increase your mastery score. What does this mean? Well it means that when you cast a spell and you have 100% mana remaining in your mana pool do do 12% more damage with that spell. So if the spell did 1,000 damage without the mastery, it would do 1,120 damage with the mastery. However; as your mana pool decreases, so does the percentage of bonus you receive to your damage.
With a 12% mastery bonus with a spell dealing 1,000 damage you would do 1,120 damage at 100% mana.
With a 12% mastery bonus with a spell dealing 1,000 damage but your mana at 50% you would do 1,060 damage (50% of 12% is 6%, 1,000 + 6% = 1,060).
With a 12% mastery bonus with a spell dealing 1,000 damage but your mana at 10% you would deal 1,012 damage (10% of 12% is 1.2, 1,000 + 1.2% = 1,012).
Understanding this concept is important as, for the most part, you will aim to keep your mana pool as close to 100% as possible in order to maximise your damage.