I just noticed an agent on Twitter with a reminder that's very important for new writers.
Sometimes in non-fiction you can get away with querying an incomplete manuscript. This is not the case in fiction (unless you're asking your current publisher which idea to go with or whether something is worth pursuing).
Always finish the book then try to sell it. Of course, you should be aware that your finished may not be your publishers' finished, but the words 'The End' should have been written. Oh, and the manuscript should be edited to the best of your ability. No, you should not do the final edits on your own work, but one of the Writerly Sins is 'Premature Submission' (or 'Premature Submitulation as the wonderful Lynn Price loves to call it) - submitting something that's just not ready. Writing a book takes time - don't rush it.