An easy way to use 4-1-4 Invoker ( 2 forge spirit plus cold snap )
Take Quas at level 1 because we can use cold snap on level 2 whenever we have Invoke. Then take Exort at level 3 for forge spirit to control or deny the rune.

Early Game:
Cold Snap is your absolute best spell during this phase. Do not level up your orb until you see your opponent and his/her items. Focus on Quas for 2-3 levels if you can harass opponent out of lane with Cold Snap; otherwise, focus on Exort to farm, Sun Strike, and control runes with Forge Spirit. There are exceptions of course, adjust as needed. You will have double forge spirits when you reach Level 9 with both Quas and Exort Level 4.

* Harass enemy using forge spirit in lane.
* Buy midas first instead of boot if outfarmed opposing mid
* Choose between force staff or dagger depends on enemy heroes.

Mid game with Necronomicon

This is an important build if your team does not have any hard carry. Quas is focused because Cold Snap and spirits/necrobook is extremely powerful. Blast and ice wall synergizes superbly with summons in a team clash.

OR

Mid Game with Eul Strike Combo:

Instructions:
Disassemble Ring of Basilius when you need Sage's Mask for EUL's Scepter's full recipe.
You can also sell Ring of Protection to build EUL faster.
Sun Strike's damage is shared among all targets within the AoE. Therefore, avoid initiating with EUL when target is surrounded by creeps.

Eul lift = 2.5 Seconds
SS Delay = 1.7 Seconds
Meteor Delay = 1.3 Seconds

Eul Target
Wait between 0.8 - 1.0 Second
Cast Sun Strike (Anticipate Blast push back)
Immediately cast Meteor
Invoke Blast and cast it when Meteor is about to land.
(Blast can be swapped with Cold Snap if target does not have good escape mechanism.)
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Late Game ( 19 level above with Aghanim and Refresher ) :
Invoke Tornado first, then Meteor
Prepare WWW for EMP. Cast tornado, invoke EMP
Cast EMP then meteor, prepare QWE for blast.
Invoke and cast Blast asap!
Refresher!
Cast EMP and blast again.

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You can train your Invoke speed at here http://www.invokergame.com/