Before you write your novel, write a synopsis. Use the synopsis as a reference guide as you write your novel. If you have clearly written details to refer back to, you are less likely to produce anomalies in your novel.
Write a description, at the beginning of your synopsis, for each of the central characters. Initially, whilst you are writing, you can have things such as date of birth or favourite colour or ten things your character hates about soap operas, as well as a physical description of each character. Edit this down, before you send it to a publisher, to a brief biography and make sure that your final sketch matches the character in the final draft of your novel.
Write a graphic description of where you novel is set. Each description should be accurate, as nothing turns a reader against a book quicker than a mistake. The more research you do the better, but don't be tempted to add all of these facts to your novel. A Certain amount of background information is what you want, anything too detailed may stand in the way of the actual story. You will have absorbed so much information, it will colour your writing anyway, making it richer.
Make sure you have your name, address, email address and telephone number on every page of everything you send to a publisher. Make sure you spell check and grammar check everything you send.
Now that you have finished your novel, edit down your synopsis to a more manageable size, about four pages. Remember to include a good description of the plot. Do not think you have to leave the hook or any surprises out of your synopsis, you don't. Make the editor will want to read your book and assure them with the synopsis that this is a book people will want to read and, more importantly, buy.