There's no one-size-fits-all response, unfortunately, but I don't think you can go wrong with
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Cultivate a regular work schedule as much as possible. Never exert yourself beyond your physical or emotional limits, but working on something every day, trying to post new work at a consistent pace is a skill of immense value and keeps you present in the minds of your growing audience
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Find something you like, that excites you and that sparks the desire to paint something but which also has a big existing footprint. This one feels cynical but being entirely honest, a huge part of my early career was built on Dark Souls, YGO, Eva and Pokemon fanart that spread like wildfire bc of the size of those audiences. I specify "that excites you" because it'll crush your soul to work on something Just For The Clicks, you gotta find the spark to pursue it. I would have painted fanart from these things regardless - but it's true they became the foundation of my online presence. If nothing appeals, don't worry about this, forcing yourself will produce nothing of worth and hurt you in the process.
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Study study study. Every life study you do, every exercise, every attempt to push outside your comfort zone will reward you tenfold, both increasing your skill and demonstrating your versatility and dedication to improvement. People love to see these and follow someone as they grow! I like to alternate between studies and stuff that feels like a "reward" for myself.
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Don't consciously worry about cultivating a niche or trying to find a "style". Literally just follow your heart and indulge in the things that you love. If you have your passions on show, the rest will come by itself, and a dedicated niche audience is often where you'll find clients, especially repeat ones.
As a final word - understand that for a long time, folks may commission you first and foremost bc they need "any" artist, not specifically you - the very first paid commission I did was a portrait of Chairman Kaga from Iron Chef, it had zero to do with anything I was painting at the time and was born purely from the client's desire to own one. Give it time, take your wins where you can get 'em. Be polite, but don't take shit. Provide revisions and adjustments on request, but limit these after a point. Hit a balance between what you can offer and what overdraws on your spirit. This job can be infuriating and rewarding in equal measures, but I sincerely love it and I hope your journey is satisfying too!