Elisa Gabert (of Dear Blunt Instrument) on that question:
There may be important and famous writers who went to the grave tortured and doubtful of their own talent. It’s possible that you can find great success as a writer without ever feeling like you “know” if you’re “good.” To me, that sounds like no way to live. So when I write, the standards I try to meet are my own: Do I want to read what I’m writing? It’s that simple. If I write a poem or an essay that I want to read and re-read after I’ve finished writing and editing it, then it’s good by my own lights.
If you don’t feel that way about your own writing, the challenge becomes: Write something that you would want to read. It may sound obvious, but I don’t think most writers hold themselves to these standards. Did you know that people are faster to recognize photos of themselves that have been photoshopped to make them look slightly more attractive? Self-assessments are often self-flattering. (It’s not easy, but I think working at being a better reader and editor of other people’s work makes you a better reader and editor of your own work too.)
Ok, I want to say, but what if my taste is no good? Or out of touch with what the journals I want to get into are publishing?
Read more to improve my taste? And hope I am capable of such improvement.
Here’s the entire article, which is very much worth reading in its entirety.