Research the appropriate market for your book. Do not waste your time approaching a publisher who specializes in lifestyle non-fiction, with your novel. No matter how good it is, she is most unlikely to be interested. Study the market, looking in writers' yearbooks and digests and even on the bookshelves for similar books to your own, so you can check the publisher.
Look for the publisher's guidelines on the relevant website, when you decide on a publisher. Follow any instructions to the letter. The publisher may ask for a proposal, three chapters and a synopsis. If that is the requirement, then that is what you must send. Do not decide that your last chapter is better and send that instead. Give careful attention to your proposal and synopsis as these create the important first impression.
Present the manuscript neatly and professionally. Ensure there are no typing errors and that there are no marks on the pages. Number the pages. Always use a standard font, white paper, black ink and double spacing, unless advised otherwise. Do not staple your pages together. Include a front sheet with your contact details. You could also include these on a header throughout the manuscript.