Characters that grow and develop and make new mistakes, which trigger new stories!
In series novels like Discworld, I love references back to previous works. (I also love the digs at things on our world too!)
It being accepted! Successes do breed confidence. Confidence helps your writing.
Feedback (critical and positive) via sites with good reputations like Shortbread as you learn a lot from things like this. Also contribute as it shouldn’t be one-way traffic.
Witty characters who grow on you, who come up with memorable one-liners, who live on in your imagination after the tale ends.
Seeing work improve and read better as I edit. I should be able to sense the work “tightening up”.
Being able to tell my characters apart thanks to their use of language, style of dress etc
As I write more, I’m filling in mental pictures of my made-up worlds. Ironically it helps make my world seem more real. I like that.