Simple answer: you don't.
Most often editors do not go into detail about how you can improve your chances of being published. It gets too complicated. Editors are often too busy and cannot make a habit of critiquing every story they receive. It isn't their job. Workshops are designed for feedback. An editor's job is to read through submissions and find stories that fit the goals of the journal they work for and to then collaborate with authors regarding any changes the stories need before publication. Some authors do not agree with an editor's decision to cut this or that from a story, so the authors may withdraw their work and submit elsewhere.
Rejection is never easy. Well, not usually. Not for most people. Some authors keep an office wall covered in rejection slips. Others don't care so much about the slip itself, but still take the rejection to heart. If a writer has 'darlings' then stories are held personal and close to the heart, which makes rejection more difficult. Feelings, actually, make rejection harder to bear.
Think of rejection as an opportunity instead of something personal. Think of the story as a separate entity, instead of an extension of yourself. For example, when I write a short story I know it must stand alone. A story I've written must have many qualities that make it not only a story, but a good story. So, each time I think I've finished a short fiction piece, I must ask several questions about it, such as is it even a story?
"Of course it's a story! I wrote it. It must be good. It's about something wonderful and I felt good writing it. It doesn't need any changes."
The more I've learned about writing, the less attached I've become to my work. I've learned to let go. I've learned to let my stories live on their own. This has meant making a lot of changes to a story so that it 'works'. Many times a finished story will be so different from a first draft that no one would know one came from the other.
Back when I was studying fiction, my professors talked about how a good book of fiction, including short story anthologies, could take five or more years to write. Imagine all that submitting and the rejections, over and over again. Even established writers receive rejections. They know there are no secrets, except hard work and, perhaps, a mind open to learning and growing. For example, an experienced writer may have an increased chance of being published due to his/her knowledge of the writers' market (which journals publish a particular type of writing, for example). An experienced writer will also know to follow guidelines, since the more esteemed a journal becomes, the more selective they can afford to be. Many journals reject submissions based on formatting errors alone. Most of all, an experienced writer knows what makes a story work.
So, you won't know which story will be exactly right at any given moment or when a story will be accepted by a literary journal. The good news is that you have a lot of options when it comes to writing a story. If a story is rejected by a journal, pay attention to the stories being published by that journal. Ask questions about those stories (for yourself) and find answers to those questions.
Examples of questions you might ask when reading published stories, or reworking your own drafts:
Why is it a story?
Where does conflict occur?
How is the story rich in detail?
Why can the story be reread two or even three times and be interpreted differently or more thoroughly on each read?
Why does the moment when the story takes place make sense/why is it the perfect moment for the story (or is it a story at all)?
Why does the first paragraph make you want to keep reading? (If you don't keep reading, then an editor probably won't either. But if the story is published, reread and try to figure out why the story is considered publishable material, even if you don't like the first paragraph.)
What makes the characters three-dimensional?