Things I've learned so far as a small artist on The Internet TM
The old adage that fanart = growth is true. It's annoying if what you're most passionate about is your original work, but it is what it is. The fanart doesn't even need to be that "good" though, either. You don't have to fully render it for it to get attention. Even a messy sketch or a flat render of one character could end up doing really well. Once you've grown your follower base through posting fanart, your original art will tend to get more attention.
No shame in reposting work if it flops. No shame in reposting it again if it flops a second time, or a third. Sometimes something won't get attention until after you put it out there a few times and it's fine to keep trying until it finally clicks with an audience and gets reshared consistently on a regular basis. Also by "repost" I mean re-uploading the whole thing entirely, I've noticed it's more likely to get you more engagement as opposed to resharing (read: retweeting, reblogging, etc.), resharing for engagement I've noticed goes better for artists who already have a larger following.
No shame in attaching links to other social media, shops, etc. on your posts. You don't look like you're "selling out" I promise. If people are interested in purchasing their work, but they don't know you have anything for sale... then you're probably not gonna make much sales.
Going off of the last point, I know influencers and corporations have turned advertising and marketing into something that feels so damn disingenuous and greedy, but if your goal is to make a living off your work, you kinda have to do it. I know it feels gross, but you're not likely to get anywhere (unless you're lucky) if you don't. If it helps you feel any better: a "grifter" is what we call a person who already has too much money than they know what to do with trying to make even more money because they're a greedy bastard, or a talentless schmuck who is trying to make the most money they can doing the bare minimum because they don't want to work an actual job. You aren't going to look like a beggar for advertising your services or products, I promise. If you are good at what you do and deliver quality results, you're already doing better than most sellers on the internet right now.
Any social media that has a "group" or "community" feature, use it. Even if it seems like it's a pointless feature, even if it doesn't seem worth it because the group is small, people do pay attention to them and it does get your work more visibility.
Short-form video content is what the algorithms of most social media platforms reward you for making now. It sucks, I know, I hate it too. You should be able to post a photo on a platform whose foundation was built on photo-sharing and have it get a fair amount of attention without making it into a video, but it is what it is. The art alone might not get engagement (not even from your followers), but the timelapse of you making it likely will. Videos on average will get you more views, likes, shares, and followers on a consistent basis (even weeks or months after uploading it) than posting an image. Uploading a speedpaint as a YouTube short will do better than uploading it as a full video. TikTok is surprisingly good for visibility. If you need to advertise something, make a video version in addition to an image version. All in all, short-form video content is a good pathway for growth even if you're starting out from 0 followers.
On a similar note to the above: if the platform has a "story" feature, use it. It is another small thing that boosts your engagement, and your followers might not even see your new post unless you share it on your story.
Sometimes the time of day you post something matters. Some platforms have more users active either at morning or night, and the hour you post could be what determines if it gets seen or not. This kind of data is easy to find online for any platform, and it may also shift frequently. This is what queues and scheduling posts are for.
The frequency of how often you post also matters. Posting consistently matters more than having a lot of work available to post at one time. If you're starting fresh on a new platform, it might be better for you in the long run to post once a day, once a week, or biweekly than posting everything you have available at once. Depending on the platform or what you're sharing, it might even be ok to post only once a month. That way, if you're the kind of person who doesn't have the time to be constantly making new art on a regular basis, you don't have to be. If you have nothing to share a certain day or week, then it's okay to repost or reshare an older piece instead. Posting a lot at once may actually be WORSE for your engagement because the algorithm might recognize it as spam. This is also what queues and scheduling posts are for.
Cast a wide net. Don't knock a platform until you've tried it. DeviantArt is considered "dead" by most, but I still use it because it's one of the platforms that gets me the most engagement. I didn't use YouTube Shorts or TikTok for a long time because I didn't personally care for them, but they're actually working pretty decently for me. The more platforms you're on, the faster you can grow your audience and get people to follow you on multiple platforms.
A bit contradictory to the last point, but still important: if nothing you post on a certain platform gets any engagement (not even a few views), don't use it. Why waste your time on something that isn't turning out results? Sometimes you just need to learn the algorithm in order to make the platform work for you, and sometimes you just got to know when to call it quits. Some platforms inherently work better in the favor of larger artists or specific styles and mediums, if they even have much of an active community at all. If it's not helping your growth, then you're probably better off abandoning it.
Going off the last point- Twitter is just not worth it anymore unless you're already a large artist or have a sizeable group of mutuals who are willing to retweet your work to boost your engagement. Just full stop. It's run itself into the ground as far as it can go. Yes I am making a point purely to shit on Twitter because it is just that awful. As a small artist starting from 0 followers on any other platform, you are still likely to get a small amount of attention on any upload at the very least. You cannot do that on Twitter. It's a ghost town for small artists over there, even if you're using trending tags or engaging with the community (ex. art share posts). That's not even mentioning all of the alt-right or AI bullshit. Don't waste your time on it.
"Search engine optimization" (SEO) is a real slog, but there's some method to the madness. Some "keywords" or tags on specific platforms will get you more engagement than others, and it's worth researching. I honestly don't think "mastering the algorithm" should be as complicated as it is (social media platforms are terrible at listening to their audiences about what the audience actually wants), but such is the way.
You gotta make what you wanna make. If you upload something that you didn't actually enjoy drawing, it's gonna show and people are gonna tell. Yes, this goes even for things like fanart and trends. Don't draw it unless it's something you're actually interested in, otherwise you're just gonna burn yourself out on mediocre work.
This is more of a mental health tip, but: don't assume that because an artist gets a lot of engagement, that it means they are making more revenue from their art. Being a popular artist online doesn't automatically mean that they are doing art full-time or that it is what is paying the majority of their bills. On the other hand, there are a lot of people who are successfully making art full-time for a living, yet they don't have a big social media following at all. Remember, comparison is the thief of joy.