Before sending your work to a professional editor, I highly recommend having at least two people (fellow writers or avid readers) read over your book and let you know what they thought of it. Editors are amazing at fixing grammatical errors, sentence structure, and some will even comment on things like characters or the flow of the story, but you really need to have a few people give an honest opinion of your story to see if the concept works well.
I have had two beta readers go through my work and they have been absolute life savers. They pointed out some considerable flaws like continuity errors (i.e. forgetting one character dyed their hair and mentioning that they had their previous hue – oops!) and there were some significant historical inaccuracies I had missed, despite research. It would have been so embarassing to have my novel out on the market with such errors. Having two writers go over my work was the best decision.
Something to learn about self publishing: There is no rush.
Take the time to edit and tweak your story line until you are absolutely satsified. Then, edit it again. Have a few people do a peer edit after that and then, when everything makes sense and the details are in order, send it over to the editor.
Do you have a certain number of beta readers go over your story before sending it to an editor? Tell me your thoughts on beta readers. 🙂