There is a lot that goes into it, but I will mention just one point, often times overlooked by artists.
Social media is where you build your voice. Not your singing voice, but the voice of your brand. Your music is the core, sure, but it's only a part of what makes your identity.
You may have an idea of who you are as an artist in your head, but before you start expressing yourself publicly (so, online, through social media) – not only your existing or potential listeners will not be able to connect with your personality, you yourself may not have a clear understanding of what your brand is.
That funny joke you came up with will look odd in a tweet; no one will understand the genius behind the trash can photo you posted on Instagram; and that's fine. As with anything, you need a lot of repetitions to get good at something. And by "being good" on social media I mean "being confident". Being weird is not required. In fact, it's recommended.
But you need to understand both your online voice and specifics of a platform you're posting on before your confidence and charm start to shine through, resonating with your followers and listeners. Fitting in is not required, either, but I mention that you need to understand basic specifics of your social media platforms, as I've seen quite a few cases where artists' weirdness appeared as ignorance to others. Learn the etiquette.
I've seen artists to whom being active on social media comes naturally, and I've seen artists who have learnt it over time. If you are struggling with social media, you should know that you can do it. You just need to start ASAP, even if no one's reading or watching.