Selling a book, particularly for a new writer, is a bit easier than
selling snow in the Arctic.  If you want to have a good chance of doing it, make sure you meet the following requirements. 

WHAT A STORY IS, AND HOW TO WRITE IT. 

What follows considers the determinative, architectural method of making a story.  Some writers do it all with inspiration.  If all architects built houses like that, most of us would be homeless.

This kind of story needs a theme, a problem and characters to wrestle with it all.

A story consists entirely of a problem.  The story begins when the problem begins.  If the problem ends, the story ends.  The only way for the story to continue beyond the problem is if you introduce another problem.  Even stories with ten problems, one after the other, are at an end when the last problem is solved.  Some stories, like Gone With The Wind, end with the central character facing another problem. 

The secret to problems in a story is that they get harder, not easier, as the book goes along. 

There are two secrets to characters.  First, if you can select four people you and somebody else know, then write a practice short story about them, changing their names, and your somebody else can read the story and identify all four, you have learned how to create a character out of words.  (If they can identify the people just by their dialogue alone, you have a gift.)  

Secondly, if the characters you select for your book would prefer not to have the problems in that story, but feel compelled to get past them, anyway, then you have something really good. 

The theme of a book is the message the reader gets when he finishes reading the last word.  The theme of Ernest Hemigway's Old Man and the Sea is as follows -- a man is not defeated until he accepts defeat.  If you don't quit, and even if the great fish you catch is stripped to the bone by sharks by the time you reach port, you have not been defeated.  This is what is meant by victory in defeat.  Honor results from the spirit of the man in the fight, not the outcome. 

The first sentence of that book is perfect.  "He was an old man who fished alone in a skiff in the gulf stream and he had gone eighty-four days now without taking a fish."  It physically identifies a sympathetic hero, establishes the dimensions of the playing field and presents the terrible problem he faces. 

Hemingway wrote that book for you. 

When you have the above figured out, then do it.

You must keep on keeping on.  When you are stuck in the morning, begin by writing anything, and keep writing it.  It will kick something into gear and get you going.

Write anything.  The quick brown fox jumped over the lazy dog because the farmer was firing at him with a Russian Kalishnikov automatic he bought from a passing Orthodox priest who was wearing a camoflage cassock and singing a tune by Bob Dylan, who had smoked so much grass and got so high that he was the first man on Mars, where he discovered a McDonald's that served Gooran Burgers with a side of antennas.  

Anything.  Usually, your story will start to appear in the zany text, and you're off and running.

How do you know when the book is done?  Easy.  When you've answered the question posed on the first page.  If your story is about how a particular boy becomes a man, the story is done when he becomes one -- unless in doing so, an even greater problem now faces him.  In this latter case, make sure the question on the front page contains this second problem, too.  That would make your front page theme statement - Does becoming a man solve a boys problems?  Or, it could be - Be careful what you wish for, because you just might get it.  

When should you edit your story?  A chapter or an entire book, after you've written it.  Write in hot blood and edit in cold blood.

Now, as to sending stories out.  Short stories you mail complete.  The whole manuscript.  You include an S.A.S.E.  Books, you send the first page of the first chapter and a one page, three to five paragraph, description of the entire project.  In either case, they must be double-spaced, include your name and address and word length on each page.  Do nothing else.  No fancy type, no pictures.  If it's an illustrated book, include one of those.

Who do you send them too?

Go to a book store or a library and hand those two pages to an official litereay person.  After they've read them, say, "Who publishes books like that?"

If they say, "Nobody. This is junk," get two more opinions.  If one of them gives you some publisher's names, do the following.

Then get those addresses from Writer's Market (a book about companies that publish writers) and look at their listing.  If it says they take cold (non-agented) submissions, send those two pages to them, one publisher at a time, with an S.A.S.E.  Then, start another story while you're waiting to see what they say.  Keep writing new stories and keep sending out the completed ones.  People have sold books after sending them out for ten years.

Writing is hell, editing is hell, rejections are hell and sometimes even success is hell.  Hemingway once described the ordeal represented by that first blank piece of paper in the typewriter. Here's what he said.  "It is facing the white bull which is paper with no words on it." 

If you can do all that, then you have met Ernest Hemingway's definition of an author.  You will age prematurely, lose most of your friends and probably starve to death.  Before you do, your marriage will dissolve, your children forget what you look like, your bank account will disappear and you will find yourself sitting at your desk looking at a fifty thousand word manuscript that you suddenly realize is a piece of crap.  Most likely, you will begin to weep.  I once knew a writer who had been a boxer.  A light-heavyweight.  He was undefeated in twenty professional fights.  He took up writing.  When he arrived at that point, at that table, and realized his manuscript, his years of work, was a piece of crap, he bawled like a baby. 

Then, he picked up a blank piece of paper and put it in the typewriter and began a new story. 

His name was Walt Morey.  His most famous book was Gentle Ben, and it was made into a Hollywood movie and a television series.  When he died he was worth seven million dollars, and didn't care a whit about that.  The last time I saw him, just days before his death,  he was trying to figure out a story. 

Good luck.