Two rune spawns has made the game harder for Invoker. It is now more difficult to contest runes. Even with forge spirits, Invoker cannot guarantee a rune deny for bottle holders.

Lane Phase
Cold Snap and Tornado will be your primary spells. Make sure you get tangos/clarities as needed. Always carry TP scroll after boots! Because Invoker has slow starting MS, try to secure top Rune, but don't force it.

Early Game
Contest runes as you see fit. Avoid initiation at this point. Cold Snap, EMP, Ghost Walk, and Tornado are your primary spells. Tornado is great if you need it to disable buffs (Ursa, Ember, Drums, etc). Ice Wall is your secondary spell. TP secretly as needed.

Mid Game:
Your moment to shine! You can kill most heroes solo, scout, coordinate ganks, and team fight. Puck, TA, Weaver, AM, etc will hate you for the orchid, urn, snap, emp, and ghost walk! Be cautious about sentry wards, you may get baited. Moreover, Ghost walk's slow reveals your general location.

Late Game:
Don't be afraid to use Alacrity on spirits before battle. Harass tower/racks with your summons.
Here are two popular strategies:
1) Stay in Ghost Walk and pickoff a vital target like Enigma in a team battle. Proceed to crowd control with Blast and Tornado.
2) Initiate or counter initiate with Tornado, Meteor, Blast, then proceed with Alacrity and chase with Ghost Walk + 3 Wex.

Very Late Game:
You desperately need to end unless you have a good hard carry. Invoker is a great late gamer, but he cannot compete with hard right clickers like Void, Medusa, Spectre, etc. Magic Immunity is also a big pain, but at least you have spirits, and alacrity. You even have tornado, blast, and ice wall to disable the ones without magic immunity.

For more details on spells, strategy, and important tips/tricks, see my comprehensive guide after 6000+ games at:
http://steamcommunity.com/sharedfiles/filedetails/?id=185528211#

Votes/Comments are much appreciated.