Some authors get all uptight about other people messing with their perfect prose. It's not a matter of them saying Starbuck is better as a female than a male character. It's a matter of them saying you missed this, that, and the other. Oh, and by the way, you can tighten this up, expand on this, whatever.
The other important thing is fact check, fact check, fact check. Stupid mistakes happen. In my weird western, I incorrectly referred to the hero's mare as a male. Several times. If your characters happen to use weapons, whatever they may be, make sure you get your phrasing straight. Because there's plenty of people out there that know more than you. And nothing will take the wind out of your sails more than when your ninja assassin uses an english broadsword, and you get caught. Or John became Jim who later became Jeff. Or your main character has chameleon eyes that change from blue to brown. Unless, you want your character to have chameleon eyes.
Those are things an editor is paid to do. And they do it well. You can get by on beta readers and stuff, but it never hurts to get a few more eyes, even if you sold your firstborn for one.
The other thing is check out getting a professional cover. Have someone double check your copy, find a couple of people you respect and see if they'll blurb.
i just found some software today "book cover pro" that I may download the trial version of and play with. Looks great for making decent covers for print media..