Most importantly, start by making sure your work is free of mistakes in spelling and grammar and that everything's clear. For this step, classes or writing groups are helpful. Your stories may have problems that you're not aware of. And even if you don't trust other people with advice on critical elements such as plot or character, they can point out grammatical problems or points of general confusion. At the very least, read through your story with an editing checklist at your side.
Finally, have more than one story ready for submission in case an editor asks to see more work. Once you have his or her attention, you need to follow up right away.
