First and foremost, focus on having a good story (and good art, for comics). You can have the best promotions out there and still never retain viewers if your story is boring or uninteresting. Try to have a catchy first chapter, some strong cover art, and a description that makes readers want to take interest on your work. These set up the basics for what you can promote elsewhere, and they encourage on-site viewership from people scrolling through Tapas.
After that, my most successful means of gaining viewers has been interacting with the community and posting bits of art or storytelling to discuss with others. (This does NOT mean just posting promotions over and over.) Talk to other creators and readers, join Discords for people interested in the same topics as you, and be open to talking about other people’s works.
Plain ol’ advertising is also useful. You can post ads in Discord servers, or you can use sites like comicad.net to display banner ads across the web (for super cheap). Create attractive ads that are visually interesting and make notes of what your story is about.
Social media is a HUGE one. I personally don’t even use most major socials, but I still get a ton of viewers just from Tumblr. Post frequently about your creative process and when your readers can expect updates. Learn to take advantage of popular tags.
Lastly, just be patient. Focus on your story instead of its success. I started my comic in July 2023 and I’ve only got 5000 views, but from those views I’ve got 277 subs and over 500 likes. That’s a pretty good ratio, and I’m very happy to have anybody else enjoy my story at all! Create what you want to create, engage with the community, and find what works best for you.