A good initial strategy is definitely rooted in social media: cross-posting on genre/engine-relevant FB groups, joining and interacting in fitting Discord channels, hijacking the bigger #'s on Twitter (and Insta to a slightly lesser extent) - #ScreenshotSaturday #WishlistWednesday #IndieDevHour etc. But content is of course king; don't expect success here without strong assets from your game. Virality won't come out of thin air.
But there's a ceiling to social media, and you'll ideally leverage press and influencers to burst the bubble and reach a wider audience.
Once you have a following and an interest in your title, you can then start leveraging your own channels to better effect - your store page(s), website and mailing list, primarily.
There's more on all of this - specifically focused on getting results without budget - in our book The Zero Budget Game Marketing Manual:
https://svperstring.itch.io/game-marketing-manual
Hope that helps!