With visual art, I have a reasonable sense of whether what I'm doing's any good or not (by my standards, anyway). I generally have a picture of what I'm trying to achieve in my mind, and I can measure what I've actually managed against that.
With poetry it's less certain - sometimes I can pick out awkward bits, vague bits, bits that I think work, and those that don't quite come off; and sometimes I honestly don't know whether what I've written works or falls completely flat (sometimes, of course, it can do either depending on the reader).
Now, as I try to write a proper story for the first time in years, I find that sense of whether what I'm writing is good or not even vaguer. I mean, at a basic level I'm at least competent. I can spell. I can write grammatically correct prose (with colons! and semicolons! and everything!)(and ignore those rules when I want to for effect). I can (I hope) write dialogue which isn't clunkily unrealistic, avoid excessive cliches, use imagery, be aware whose point of view I'm writing from, produce - in short - something which isn't actively badly written. And, in what I've displayed of my prose to date, I can spot sentences I'm not entirely happy with, paragraph transitions that jar - in other words apply basic quality control, which is what I'm planning to do more strictly on this piece.
But beyond that, I simply don't know how to judge (or even if I can judge) the quality of my writing. How can I tell whether I've written something vivid and moving and interesting (or even one of those), as opposed to something workmanlike that slides out of the reader's memory as soon as it's finished (or worse, that they abandon halfway through because it's simply not rewarding enough)?
I'm not seeking reassurances about the quality of my writing - let's face it, if you're reading this you're already heavily biased in my favour anyway. But if any of you many writers out there would care to share how you deal with these uncertainties, I'd be very interested to hear.