Read the Darned Guidelines
Because the average publisher doesn’t have time to answer every individual’s questions, we put a great deal of effort into writing the guidelines. Therefore, it tends to irk us when we don’t believe authors have read them. (How would you feel if you put up a "Keep Off the Grass" sign and I stomped right over it?)
The guidelines are there to let you know what we need for the publication, what we’re looking for, what we’re not and how our vetting process works.
The main character must do something. The MC meets an obstacle, no matter how subtle. The MC either overcomes or fails to breach the obstacle. Perhaps he or she wins, but at a horrible price.
Regardless, of the outcome, the character’s life has changed because of the events in the story. (There are only so many nihilist stories that the average reader can stomach.)
If I were to interview your MC, what would they say? How would they react to personal questions about their past? How about their loved ones? What values do they have that they are willing to die for? How has compromise affected them in the past?
You should know far more about your MC than the reader, but give them enough to form a relationship – even in short fiction.
This doesn’t mean to spend three paragraphs describing a blade of grass (*cough* Jean M. Auel) or what Lorraine looks like in her dress. Rather, the best writing incorporates the descriptions actively and naturally.
You must pay attention, not only to grammar and punctuation, but to the flow of your language as well. Read it out loud. Have someone else read it out loud. If you, the writer, are stumbling over words, the reader surely will as well
Most (but not all) publishers prefer authors to use Shunn’s Manuscript format (http://www.shunn.net/format/story.html)
Using crazy fonts or a specialized version of Word or WordPerfect may make it difficult to impossible for the editor to read. Guess what, if they aren’t enjoying the reading experience, they likely to enjoy your story, no matter how well written.