Thanks a bunch for posting this! I've had moderate success self-promoting on twitter, reddit etc. Reddit definitely reaches an audience, if you post something that catches people' attention. #screenshotsaturday generally seems the most successful tag when I post screenshots or GIFs of my games. I use Game Maker and YoYoGames tends to post every saturday asking what people have done that week, it's a good place to post your screenshot saturday (if you use Game Maker that is!)
Otherwise itch.io has a dedicated announcement section: https://itch.io/board/10022/release-announcements - the moderators on itch check these posts regularly and if you luck out, you can get a feature spot. From my experience being on the front page has the most definite impact, so make sure you polish your announcement! I tend to follow the guidelines to the letter with description, GIF, screenshots etc. Here's an example with my latest game.
Dev logs work too, if you make a major update or launch post. Check out that post from the itch creators: https://itch.io/updates/devlogs-post-types-enhanced-browsing-and-more. Check out the "A New System For Updated Games" section. Definitely worth keeping in mind!