Write an outline for your novel. It doesn't need to be detailed. You can do this by hand or with your word processing software. Write the outline in Heading and Subheading format. Label the main headings as chapters or chapter names. Use the subheadings to outline the key plot points within that chapter. Having an outline in front of you while you work is a good way to avoid running into a block.
Create a short biography for the main characters in your book. The bio should contain physical descriptions, likes and dislikes, education history, character defects and any information in the character's history that will be pertinent to your book. Don't be afraid to include material you might not even use in the book. The more information you include, the easier it will be to write about the people in your book.
Bring out your outline and work from it, but don't be afraid to stray from its course if the story seems to be heading in another direction. The outline should never be rigid.
Set a reasonable daily goal for yourself. Write 5 pages a day 5 days a week. This is a reasonable goal that will produce 25 pages a week and 100 pages a month. It won't take long for your book to come together at that rate. Don't review your work at this stage.
Print out your manuscript and find a comfortable chair, grab a pen, and starting reading the first draft of your story. Mark problems with dialogue, story structure, consistency and any typo or spelling errors you find. The first draft will be full of corrections. Once you've gone over the manuscript, return to the computer and begin writing the second draft, incorporating the notes and changes you wrote on the first draft.
Print and read your second draft. This time you should be reading as a reader. Try to read the story with an open mind. Make a note of any typos you find. There shouldn't be too many story problems because you took care of those in the first draft read-through. Return to the computer and correct any typos or spelling errors.
Get someone to read your manuscript for you. Preferably, this won't be a friend or family member unless you're certain they will be extremely honest with you. Let them read the manuscript as a reader to see what they think of it. Also, another pair of eyes for typos is helpful. No matter how conscientious you are, errors can still pop up by the third reading of the manuscript. After the third draft has been read, correct any errors your reader found and incorporate any changes they suggested that you feel are valid. Now you're ready to shop the book around to publishers.