Although there are dozens upon dozens of varying techniques of editing your stories, for the most part they can be broken down into two camps: macro-level and micro-level editing.
I'll break these down further in the subsequent blogs, but here's a teaser of them right now.
Macro-level is the overall story. This could be the tense of the story (past or present), or the structure, the plot, characterization, descriptions, or even what I call the "realistic-ness" of the story.
Micro-level is the bits and pieces of the story. This is each chapter, paragraph, or sentence. This would also deal with the plot, characterization, and descriptions, but on a more individual basis.
When I'm editing, it feels like my mind is scrambling on various planes, on both the macro- and micro-level. This is why it typically takes a writer a long time to get their story publish-ready, because there are so many aspects of writing you need to be aware of.
But rest assured, with practice, one can learn these and become a better writer. You'll still need the assistance of a great editor. Nothing could ever replace that. Yet the more work you can do ahead of time, the better.