Five things you may not know about the world of publishing . . .

1. You go into a bookshop and browse the titles in the chart, then choose one because after all, it's in the bestselling section so must be good, right? It may well be, but bear in mind that publishers pay some bookshops money to have a title displayed in the chart (and indeed in special offers and beautifully laid out on tables). What you are buying into is good marketing.
2. Not all published authors can write, at all! If you've wandered into your local bookshop and picked up a new book by such and such celebrity, chances are it has been 99.9% ghostwritten by an invisible and uncredited writer. In my time, I've done this on one book which shall remain nameless, and found it a very frustrating, badly paid and unrewarding process.
3. Not all published writers can write well. Rumours abound that some of the highest-earning authors in the world are actually poor writers who scribble out ideas which are formed by a good editor. In my job as a proofreader and editor, it's astonishing how much work I have to do on material written by 'proper' journalists, copywriters and authors.
4. By a certain point, some publishers will give up on perfecting text in the rush to get it printed. Once text has been typeset, changes take time and cost money, and proofreaders may be instructed to only pick out the 'worst mistakes' and ignore the rest.
5. Some publishers don't seem to give a Dickens about the state of their text - I recently bought a best-selling book and was appalled at the amount of mistakes that jumped out at me. The odd one or two is standard - after all, no editor/proofreader is perfect - but this was up to three a page in places. Sad as I am, I began marking them up, and finally sent the corrected book to the publisher in question suggesting they may need a better proofreader. I'm still waiting to hear...

Proofreading/copy-editing before approaching publishers . . . it's essential.

Occasionally, I'll come across an author who'll tell me the following: I don't need to have my book proofread or edited before I send it out to agents and publishers. I know it's great, and I've proofread it myself and caught all the mistakes. Besides, there's no point doing too much to the text as the publisher will have an in-house copy-editor and proofreader who will do all that for me. Why should I pay to have someone work on the story or style and weed out any mistakes when the publisher will do it for me? It's a waste of time and money.

Gently, I have to break it to them that this approach is very, very, very unlikely to result in a published book. Firstly, you're unlikely to get past the slush pile if the publisher's reader is faced with typos, inconsistencies and issues in the style and content. A rare few may get through this on the basis of being a fabulous idea, but not many - what publisher wants to spend the time (and money) weeding out all those basic problems? If your book is littered with mistakes and problems, these will stand out a mile to the publisher and put them off greatly.

Secondly, you want the publisher to be impressed by both you and your book. They want to deal with a professional writer, and presenting an error-free manuscript is the ideal way to convey this. It's true that some books you see on the bestseller lists have been heavily edited and proofread in-house, but if you want to sell your book to a publisher, why not save them much of that effort?

Finally, no matter how well you think you've edited and proofread your book, unless you are a professional writer and editor, I can assure you there will still be mistakes and problems. You're too close to your own book to see the issues, and a professional proofreader and copy-editor will be looking for things you may never have thought of.

By all means edit and proof the book as much as you can, but if you are serious about getting that book published, let an expert take a look as well.