1) Tell a story as only you can tell it. Be familiar with other writing in your genre, but don’t imitate anyone else. As an editor I look for an original approach and a distinctive voice; something to set a story apart from all the thousands I’ve seen before. Surprise me!
2) Make your characters so real that the reader can tell them apart just by the way they act and speak, even when you don’t specify who’s speaking.
3) Pay attention to the rhythm of your prose. Vary the length and structure of your sentences (unless, of course, you use short, choppy sentences or long, rambling ones to make a certain point or define a character.)
4) Don’t assume that grammatical constructions you see over and over must be correct, or should be used over and over. There’s no need for sentence after sentence, or even paragraph after paragraph, to begin with a participial phrase such as “Opening the door, she crossed the room.” Think about that. Is the room so small one could cross it while still in the process of opening the door? Even when there’s no such grammatical problem, overuse of “ing” looks amateurish (and is, obviously, one of my pet peeves.) There are other more varied ways of avoiding too many sentences that start with “she” or the character’s name.
5) And speaking of pet peeves, particularly when dealing with erotica, PLEASE be sure you know whether your character’s movements and actions are physically possible. I’m not talking about superhuman endurance, or strength; I’m just considering logistics. Remember whose various parts are where, and don’t tie the reader’s (and editor’s) mind in knots trying to figure out how what was up is suddenly down, and why what faced one direction (and was, in fact, tied that way) is suddenly available for full frontal play. This sort of thing can apply to any scenes of concentrated action, erotic or otherwise, but interrupting the flow of a sex scene is especially, well, frustrating.