My first book, A RECONCILIATION WITH DEATH, was self-published. It was a clumsy process and I had no idea how to market myself. Now, I have a much better idea and am not afraid to interview on podcasts, message people directly, and advocate for my art!
It's not difficult, per se. There just needs to be a grand amount of empathy. Most characters you write will never have the same experience as you did.
Self-awareness; the ability to pick up on self-imposed patterns and know when to switch things up. Also, knowing which details to cut. An author should always be aware of bloat.