If you already published it could be difficult. The initial release helps most with garnering readers.
Two rules for that:
1. Have something that draws interest. That means in itself two things. One obviously being that your story should be something that makes a reader intrigued. Either you have a cool-sounding synopsis or are one of those who utilize a popular trope (the latter not being my favorite). Whatever it is, you need to somehow have enough to show that makes them want to give it a first look.
The other, far more concrete factor, is having something to show. Never start only with a single chapter (I'd say minimum 5). You need to have enough that a reader who may show interest can develop a "feeling" for your story. Based on this, it decides whether or not they may stick with it. If you don't even have enough to show, you can't expect them to stay with you till you get to the actually good part. Bear in mind, those early days (or maybe only one, depending on how many others release right after you), where you have exposure on the frontpage is your golden time. You'll never again have so many not-yet-affiliated eyes on you. This is the time you use to build a foundation. If you can find a decent number, the stone will roll by itself. It may even snowball if you can get a trending.
2. For the first week, each day a new chapter. People need to see you keep on posting. Maybe a bit less works, but bear in mind, most initial releases get dropped. Readers know that, and so you have to prove to them that you're still supporting your own work. After that, communicate believably with a strict schedule that you'll continue posting. At least once a week. Longer and they'll question how serious you are about this.
3. As I said, after the initial release, you may have trouble getting the same kind of exposure. After that, you may either have the power of word of your fanbase or bank on the time your chapter cover will be seen on the front page with your chapter release (which is a poor bet).
The active stuff you still could do is getting a shoutout from an established author. If they'd show a link to your story on their chapter release, all of their readers will see it. That's again exposure. Yet you'd first have to get one so far, and if you have nothing to show for yourself, simply begging won't work (The same as all the other tactics solely focused on somehow drawing people in without anything to back them will usually get ignored).
Therefore, a good base is still the most important factor.
