When writing a story there are several stages before you can call it a finished product. The first stage is often brainstorming about the concept and then coming up with the general idea what the story will be about and what it leads up to.
Then there is the first draft, where you’ll find out if the story resonates with you or not. My rule of thumb is: if I cannot blast through the first draft, or if I get stuck more often than I feel necessary, then I abandon that story because I don’t think it’s worth the effort.
That may sound counterproductive, or even lazy, but you have to realise, ideas are at an abundance. Creatives do very rarely have to fear what to write next (at least I’ve never had to fear it) because we come up with new ideas every day.
In any case, when the first draft is done, then begins the hard part. The first edit, the second edit, the third edit, and so on; you can go on like this forever if you’re not careful.
As creatives, we constantly want to do better and we do become better over time, which means that if we choose to, we can edit stories forever. So how do you decide when it is done? There is no right answer to this, but there are certain milestones in your process of writing your story that you should look out for.
When you feel that this is as good as your story is going to get, then you stop writing and set it aside for a week or a month before getting back into it. The main reason for this is that you’ll almost instantly think it’s garbage if you get down editing again and you need to distance yourself with your story at some point – might as well do so when you still think that you’ve done a good job.
When you later come back to your story you’ll have a fresh mind and you’ll have improved without knowing it. Instead of mulling over your story trying to fix small things that perhaps never needed fixing, to begin with, you’ll have come up with new ideas and approaches during your hiatus.
This is the process I work with when writing a story and I hope this will help you too in your endeavours.
Of course, there are endless variations to this, so try and find what works best for you.
PS: I realised later that I really didn’t answer the question stated in the title, but I think, in essence, when you still learn and approve rapidly, you are never ready. Only when this learning curve mellows out will it become apparent to you when you are ready to publish.