Getting your idea turned into a book that is written and published is more than putting words down on paper. It requires professionalism and standards that are expected by all modern publishing companies. Basically, if you don't follow certain rules, your manuscript will hit the garbage pile without being read.
Write an outline for your book. An outline keeps your story on track. Your outline can be a simple list of occurrences or ideas for the book, or it can be as detailed as a time line.
Write your prose. The hardest part of writing a book is sitting down and actually doing it. An average adult book runs between 50,000 to 100,000 words. Publishing houses generally only publish books that fall within their word count guidelines. Research your genre by reading publishers' guidelines either online or in "The Writer's Market" print edition to find out how long your book should be.
Type and edit your manuscript. Publishers don't accept hand-written manuscripts, so you must type it out using a computer word processor. Using a computer word processor will also help you to correct grammatical and spelling errors. Set the margin to 1" on all sides, only use black 12 pt. Times New Roman or Courier font and left align your lines.
Print the finished manuscript on plain 8 1/2" x 11" white computer paper.
Use "The Writer's Market" to find publishers that publish your type of book. Make a note of the editor's name.
Write a query letter to the editor, using the editor's full name (never assume gender by addressing them as Ms. or Mr. Editor). In the letter, introduce your book. Tell them a little about it and ask if they would like to read the manuscript. Also, tell them of any relevant publishing credits that you have. This letter should not be longer than one page.
Send your query letter to the address and wait for a response.
Repeat Step 5 through 7 until you get a favorable response.