It is now more difficult to contest runes. Even with forge spirits, Invoker cannot guarantee a rune deny for bottle holders.
Forge spirits, cold snap, and Sun Strike 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. If mid opponent is gone, you can clear creep wave with alacrity, and draw incoming creeps away with forge spirits. At least 30 seconds if attacking tower with alacrity!
Contest runes as you see fit. Avoid initiation in a battle royale. Cold Snap, spirits, ice wall, & Sun Strike are your primary spells. Tornado is great if you need it to disable buffs (Ursa, Ember, Drums, etc). TP secretly as needed.
Your moment to shine, but this build's primary goal is not to initiate. Take towers and let your team lead. If you must initiate, do it with Tornado and/or Ice Wall. Double Spirits, Urn, & Snap is very deadly at this point! If opponents have great crowd control, target the fragile hero with spirits, urn, and snap. Blast or Tornado can counter-initiate. Alacrity is great for taking towers, but it will cost you a spell rotation.
Don't be afraid to use Alacrity on spirits before battle. Harass tower/racks with your summons. Your main job is crowd control, so don't stand in the front line unless you are initiating. Always have spirits before battle and pay attention to their cool down. Tornado/Meteor/Blast is a great combo, always consider it.
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.