From what I've seen a lot of the orchestration around launching a game should be done before you launch the game. You should be building interest around the game a soon as you have something you can show. Steadily release teasers: screenshots, gifs, and videos. Sure you can get lucky and go viral, but chances are building your audience is going to take time. By starting well ahead of launch you're significantly increasing the time you have to promote your game.
In the case of itch.io, the best place I've seen for this type of this right now is Twitter. Most of the time you're creating small things like images and GIFs. It's incredibly easy to share something like that, and there's a low barrier for others to spread your tweet.
One of the goals of this forum is to be a place to promote your game as well. Looking for various game communities is a good way to find audiences as well.