This is an interesting question and I doubt most people are going to like the answers, but here we go:
So, first and foremost, you need to be realistic about why you’re creating in the first place. If you’re doing work in a fandom that is older, where content has stopped coming out, or that is simply smaller, you’re not going to get much engagement, period. There will, of course, be activity in these fandoms, but it will be far less and the people involved—while they may view your work—will be less likely to comment/spread it around simply because there’s not much going on. So if you’re creating in that sort of environment (which can be a really good environment if you’re looking for something chill with no pressure), then you have to be prepared for low engagement, even if the people you do meet and who are willing to talk about your work are more regularly in your sphere. You can probably make better/closer friends in these sorts of fandoms, if you’re willing to try.
But, on the other end of this, if you’re coming into a huge fandom late, it’s also going to be harder to wade through the massive following to get your stuff out there. For example, in both the Miraculous and Sk8 fandom, I started work pretty early on, when the shows were still gaining traction, and so my “name” as a creator gained traction parallel to that growth, as opposed to when I started writing in the Voltron fandom. With Voltron, I came in super late and so what few fics I had that did gain traction took a lot longer to get there because people already had their fav content creators in the fandom, etc. It’s not impossible to get popular in this situation—far from it—but it does take longer.
You’ll also benefit from having finished works early on in a fandom’s lifespan, at least with writing. This is because there’s less competition for views and so more people will be filtered to your work, initially. This means that you have a better chance of getting those comments and kudos. Having a finished work increases this engagement because people look for finished works before works in progress. Generally, the length of a fic doesn’t matter much for popularity, so long as it’s DONE. When I was writing in the ML fandom, quite a few of my earlier fics were shorter, and they compete in popularity with my longer fics, because people care more about having a finished story, not a long story. That’s why when it came to Only Practice Makes Perfect in the Sk8 fandom, I worked hard to get that shit done, because it was the most popular story I had in the fandom and I decided—like an idiot—to make it a long fic. Which, yeah, means people probably love it/remember it more in the long run, but if I hadn’t finished it in 2 to 3 months, I’d have lost considerable traction as far as making a name within the fandom.
This leads into one of the most important points, if not THE MOST IMPORTANT point in gaining an audience—consistency. If you do want to be a successful creator, you Have To Be Consistent. This is the most difficult hurdle for all creators, and it is oftentimes impossible to make happen. If you want to aim for professionalism, which a lot of fandom creators don’t care about (which is fine), then consistency is how you get there. Nobody wants to read a fic or follow an artist who doesn’t stick to creating what they start (RIP all my unfinished works and the people who left me as a result, LOL). Using my most recent works as an example, I very, very, very consistently updated Only Practice Makes Perfect multiple times a week. To the point where people got comfortable expecting it, which is the key variable here. When people become comfortable that you will regularly create content, they not only stick around, but will be more interactive with you and your work. Nobody likes the disappointment of getting involved with a work only for that work to rarely get updates. Most people don’t have the attention span to care. I’ll admit, if I read a fic that’s not finished and the writer takes one week to update, then one week, then THREE weeks, I probably will, like, forget about it. That’s just life.
The best thing you can do is schedule. And again, this is the HARDEST thing to do, because it holds the creator to a deadline. Most people who create in fandoms don’t want that kind of pressure—and that’s fine. I go back and forth on when I have scheduled releases and when I don’t, depending on what I’m aiming to do. But if you to retain your audience, telling them that you will update a work regularly on such and such a day and such and such a time, it creates something for them to remember. If they’re invested in your work, they will think, “oh, it’s Friday, that means such and such is coming out with something new.” But, with that in mind, you also have to commit to a schedule that people will remain invested in. Which basically means you can’t put things out more than a week away from each other, unless you’re really, really famous, lol. If I told people I was going to go on a two week update schedule, I would lose most of my audience. But a week is long enough for people to both still remember and anticipate. That’s just how the scheduling of the world works. And if you’re an artist that’s working on a big project, then you have to share progress, or pieces of what you’re doing on a regular basis. That’s what generates “buzz” and keeps you relevant. And, yeah, that’s a really hard schedule to commit to, because it’s a lot of work. BUT this consistency is where you see people being successful. Popular youtubers may not have gained their popularity by being consistent, but most sure do retain it that way. And again, there are outlying exceptions, but they generally ARE exceptions.
Speaking of hard work, here’s probably the second hardest thing to accomplish—you have to be prolific. Especially as a writer. You have to write A LOT if you want to gain an audience. And yeah, that means you have to work, a lot. I love my work, so I enjoy that “grind,” and I also have developed a lot of strategies to work around writer’s block and every other obstacle that tends to catch people up. I work in a very professional manner—I do outlines, and drafts, and plan. I do a lot of stuff that people who do this kind of thing for fun can’t be bothered with (and that’s fine), but that’s because I find it to be what works best in creating an efficient environment. I’m also very, very NOT lazy, lol. I was raised in an environment where you have to work for everything that you want. My parents didn’t buy me my first computer, or snowboard, or what have you. We were tight on money and if I wanted something, they couldn’t help me—I had to get that shit on my own. And I also grew up on a farm, where hard work was a staple of how you did things. You did things the right way, even if it was the hard way. You can’t cut corners and it’s the same with this. If you want it, you have to actually do the work, that’s it. Some people get lucky with popularity, most don’t. Most famous actors didn’t become well-known off their first efforts, they had to keep trying and keep working and then they have to continue to do that to stay relevant. So if that doesn’t sound great to you, then you might want to not focus on your audience and just create because you enjoy it, lol. Sometimes that’s what I do too, when I don’t wanna deal with the pressure.
Moving on, here’s another point that nobody is going to like. Simply put, you also have to be good at what you do. I think some people don’t realize that I’ve been writing fic for over fifteen years. I currently have nearly 2 millions words worth of fics on AO3 and that doesn’t include a majority of the stuff I’ve ever written. I practice A LOT. I write every day. And I’ll tell ya, when I started out in middle school, my stuff was not good. But I worked hard, I ignored the hate, and I kept going. That is the only way you will ever get better at anything. There’s no quick way to become a better writer, or artist. And a vast majority of people are only going to pay attention to your stuff if it’s quality work. Getting to that point is a process, on top of then creating stuff that fits into popular molds. Not only am I good at what I do (and I don’t care how arrogant that sounds—I’ve worked my ass off), but when it comes to fandoms, I rarely write “rare pairs” and “crack ships.” Generally, if it’s popular, that’s where I am. That makes a big difference and I honestly don’t have sympathy for people who write rare pairs and such and then complain about lack of engagement. You knew what you were getting into (it’s mostly the Miraculous fandom that gave me this bitterness). If you’re not writing what people WANT to read, then your audience is simply going to be smaller. And that audience doesn’t owe you their attention, no matter how frustrating it is or how good your work is. I could be the best writer in the world, but if I’m writing RekixCherry fic, I have nobody to blame but myself when nobody reads it. BUT if that’s your passion, and writing a certain unpopular thing makes you happy, then, again, you need to not be concerned with traction and your audience.
The last point I’ll make is that it matters HOW you present yourself online. A good chunk of the well-known creators in any fandom are, simply put, older people. And those that aren’t, and are able to connect with those older creators, have generally created a bubble around themselves of maturity and, like, of being nice, lol. A lot of creators are skittish these days, and if you’re an asshole (anti) or fight a lot over stupid shit, you may get a bigger audience, but you will isolate yourself from other creators. And this is important because oftentimes it is your exposure to other creators that will get your work circulating. The reason I got popular in the ML fandom? I wrote a short angst fic and a really popular artist shared it/talked about it and the rest was history. But if I’d had a habit of being an asshole, probably wouldn’t have happened. And, granted, I’m not saying don’t voice your opinions, but if you’re loud all the time, it does turn people off. Especially creators because they are oftentimes the ones being attacked. They don’t want to pull more of that negative bullshit into their lives. I’ll admit, when I was in the ML fandom, I was down for a fight, but then that’s what people came to expect, and it probably did turn others off, and then when I didn’t fight, or didn’t think the way my audience thought I should, it, again, turned people off. It’s really not worth it unless being that type of person IS your platform.
So, that’s all the advice I can give, I suppose. And even if you do all this stuff, that still doesn’t mean you’re going to be popular. At the end of the day, the thing that I stick to is this—I do what I want, I love what I do, and I work hard. If I’m in a position to worry about all that other stuff, then sure, I do, but otherwise… There’s no easy way to become popular and, quite frankly, it’s better to just “live” working hard and being a decent person than it is to focus on all this bullshit. I’ve created a working environment where I function within these “points” quite naturally, so it’s not something I think about (except for schedules, lol). Sometimes I get popular in fandoms, sometimes I don’t. At the end of the day, it comes down to how much work you’re willing to do, because you will always be giving more than you are getting back, so you have to at least enjoy what you’re doing.
Seriously, just do it because you love it. And if the pressure of everything above is something you don’t love (I like a good, high pressure situation, lol), then don’t do it that way—it’s not worth the grief.