Social media-wise, I've promoted my work on Twitter and Discord, which has kinda helped me a little bit. It's also helped to post my work to different sites -- right now, I'm only at Webtoons and Tapas.
I will say that I did get a week-long front-page promotion from Webtoons, so that did help in my readership. While I don't know how it happened at the moment, I will say that before that, I posted My Demon Valentine there and was able to make over 900 subs by myself:
I've done a few collabs with some of my fellow creators, which I think helps added to my readership:
I've also done word of mouth through people I meet. Currently, it's been working pretty well for me because people have noticed the little charms I made of my characters (with the help of user soapcahtoa of course!). I tell them about what I do, where I'm posted, and people generally take a look. I've even met a few readers who were already reading my work!
It also helps to just be willing to share your own tips on how you do comics, what has helped you learn, and other things. While there's no secret sauce, as @VibrantFox correctly said, it is important to kind build up your reputation so that people can recognize you. Maybe you're the creator who constantly helps people, or the creator who hosts collabs often: whatever it is that positively helps you and the community.
And, for personal reference, I kinda find myself drawn towards people who hype up their own work in some way. Like, they may not be this loud cheerleader that's "happy-go-lucky" 24/7, but you can tell, even if they're quiet and someone of few words, that they enjoy what they do. And that gets me hyped. Because if I see a creator liking their stuff, it makes me wanna like their stuff.