Initial Setup [Leveling Stage 1 Variant]
Your initial setup will use
Spark with Arcane Tempo and Pierce. You should be using Pierce until you spec into
Branching Bolts, at which point it can me replaced with another support.
Flame Wall can be supported with Arcane Surge, until you complete your first trial, which will grant you permanent Arcane Surge from
Constant Gale. You can try adding Fortress to
Flame Wall , but I've found it to be detrimental on bosses due to the position and spawning sequence of the
Flame Wall which delays your damage buff and makes it awkward to place properly between you and the boss.
Once you get
Raging Spirits, every cast of
Flame Wall will summon them for extra damage. This is only good in the early game.
Orb of Storms can be supported with Controlled Destruction and Execute early, for additional single target damage. You can also support it with Overabundance if you're not using
Idol of Uldurn.
Mid Acts Setup [Leveling Stage 2 Variant]
Once you get a Jeweller's Orb, add Rising Tempest to your
Spark. As long as you're regularly using your
Flame Wall, this will give you a good amount of extra damage, without any downsides.
You can also add Considered Casting to
Orb of Storms, since it doesn't affect the trigger rate, and only slows the initial cast.
As soon as you can, add
Mana Tempest with Premeditation and Inspiration to your setup. Standing in it while casting, gives you a massive damage boost, and if your gear is good enough, you can melt any campaign boss before it causes you to run out of mana.
In Act 3, after getting 60 spirit, I recommend swapping your
Raging Spirits for a
Blasphemy +
Conductivity setup. It has less effectiveness than self casting the curse, but curses have a long cast time, which means that the
Blasphemy setup can free you to simply do more damage. It also lowers the amount of buttons you have to press in each boss fight.
Late Acts Setup [Leveling Stage 3 Variant]
You can drop Pierce from your
Spark (or keep it if you find that the chain from
Branching Bolts is not enough for you) and add damage supports listed above + Acceleration if you need faster damage delivery and longer range while mapping.
When you get access to tier 3 support gems, support your
Orb of Storms with Lightning Exposure + Strip Away to apply exposure during boss fights.
In act 6, after getting 100 spirit, you can remove your
Blasphemy setup (cast the
Conductivity manually on bosses from now on) and use the
Archmage buff. This will give you a huge amount of damage if you've been working on your gear and making sure to have a decent amount of mana. Select the Leveling Stage 3 Variant to see the full gem setup above.