Your subscriber count depends on a bunch of factors.
- Do you have an existing fanbase elsewhere?
- What genre is the comic? Popular genres may help you rocket up in subs due to a much larger audience for the content present on Tapas OR it might cause you to get stuck on low subs because you're hard to find.
- Does your comic have some popular tropes in it? Stuff like isekai, boss falls for their employee etc.
- Is the style "on trend" or fashionable on Tapas? Soft-coloured shoujo manga influenced styles tend to do well.
- How often do you update? Weekly is quite good for building an audience because you pop up in "fresh" more and get frequent comments and engagement to push you up the rankings.
As Kimoi said, having a comic with really good art and storytelling does make a big difference. Though you could also say that it's not always necessarily "good" storytelling that gets noticed quickly so much as storytelling that shows some popular tropes and establishes an engaging premise within about the first few updates, because you have to engage the audience really quickly on Tapas and sell your comic to them or they'll move on. Once you've hooked them though, you do absolutely need to keep rolling out the drama to keep them engaged. Drama makes people comment, comments push you up the rankings. Engage the readers in your characters, make them love the characters, then put your characters through the wringer!
In my case, I hit 25 subscribers inside my first month of updates. If I wanted to be boastful, I could say "ha! and I did that all while in one of the least popular genres on Tapas, taking what was really too long to establish the premise in retrospect and not drawing in the sort of soft, shoujo style popular here and with a story dominated by non-sexualised female characters rather than hot guys!" ....Which makes it sound like I just did it by being awesome... and that'd be a lie. I have an existing fanbase from being in a fairly popular online video series, and from making some memetic D&D content on social media. There's not as much crossover from those followings as I'd like, but it IS there and it probably gave me a bit of an early boost.
Also, Errant isn't my first comic. It's done better than previous efforts so far, and builds on lessons from those. Very few people rocket to phenomenal popularity with their very first comic (and it isn't always good for their long term artistic development when they do). I remember languishing for months on about 35 readers for months on Drunkduck in the past with my old comics! Not only do you build lifelong fans as you make more, who will follow you to other platforms, but your work gets more polished and you get better at engaging the audience (well, assuming you work hard and listen to feedback!).