Lots of good suggestions already!
A few more things:
-Start with a longer episode. Doesn't have to be necessarily 70+ panels long, but a little something to help people get a general idea what the story is about is good. From what I can see, most comics that get a recommendation early on tend to have 1-5 long-ish episodes at the start. After the first chapter or so, you can switch to shorter updates! (note: make sure to have a consistent buffer if you want to do this. Having a good start is nice, but burnout is not
)
-Follow the Tapastry/Webtoon accounts on Twitter and keep an eye on them. Webtoon especially has those "Canvas Marathon" events that can be REALLY useful to gain more followers: they're events that last from a few days to a whole week in which readers can read Canvas series and get coins in exchange, which then can be used to unlock premium episodes. If you update during a Canvas Marathon, there will be A LOT of people online to check out free comics... and it's a very easy way to gain new followers. Granted, not all of them might stick, but a good amount of them will. During the last marathon I gained around 50 new followers. As for Tapas, the Twitter page also has events for creators, during which you may get a chance to promote your story. The new Tapastry Discord server also has plenty of events!
-Put your comic on webcomic archives such as The Belfry WebComics Index, The Indipendent Comic Database, Webcomic Library and Piperka. Some of these have some... rather outdated graphics and I didn't think they'd be much effective at first, but hey, turns out that they do work!
According to the Belfry Webcomic Index, there are about 8 people following my comic from there, and somebody even cared enough to edit my entry and add some tags to it! 
-Put a link to your comic on Random Webcomic. I know for sure that I got at least a new reader from there, so I can confirm that it works
-Last but not least: if you're already a part of a community (e.g. have a Tumblr blog, an Instagram page, whatever), share WIPs of your work to your followers to get them interested in your project. Not everyone might actually end up becoming a subscriber, but some may definitely check it out!