One of the first questions you should ask when you’ve finished your book is “What is my book about?” Try to boil it down to a sentence or two. This is the basis of plot.
Plot is what your story is about. If you just string together a group of sentences that have no coherency, you don’t have a plot. You don’t have a story. You just have words. In order to have a plot – and, therefore, a story – you have to be writing about something, preferably something that is includes conflict. If you write romance – the basic plot is: boy gets girl; boy loses girl; boy gets girl back (usually with a bit more action thrown in for interest.) Or you can think of it this way: plot is two dogs with one bone.

It is important to have a plot that draws the reader in – and keeps him or her reading. Proposing hypothetical questions the reader may ask does this. Consider the following passage from my story, “Prime Time”:
Deena studied the newest crop of lunar tourists and transports milling around the huge domed reception area as her partner began his spiel for his audience. On the far side of the shuttles, she caught a quick glimpse of Security leading out a sorry-looking group in binding collars.

One of the prisoners broke from the line and dashed for the shuttle. He never had a chance. The guards triggered his collar and took him down before he got ten steps. Deena winced as they dragged the unconscious man to a cart and dumped him. She hoped for the prisoner’s sake he never woke up. He’d be much better off. The guard glared at her and she turned away. She was here to do a job and forget whatever she might see. She could do nothing for them. Nothing.

The questions that arise are: What is Deena doing there? Why can’t she help anyone? Why would it be better if the prisoner never woke up? Is Deena a prisoner? What is going on here? Each question leads to another – and thus, the beginning of a plot.

Plot can take two basic forms, or even a combination of the two. It will usually be either a three-act structure (beginning, middle, end), or, from Joseph Cambell’s writings, be a mythic journey. It can also be a combination of the mythic journey within the three act structure.

In the three act structure, you have the beginning (Act I) in which you introduce the character(s), set the tone, establish the setting, introduce the story problem, and urge the reader to move on to the next section.

Act II is where you expand on these issues and set up the final moment of the story.
Act III is the final battle, the tying up of loose ends, and leave the reader satisfied.
The Mythic Journey, as explained by Christopher Vogler in his book (which I urge you to get), consists of:

Hero in his ordinary world
The call to adventure
Answering the call
Tasks and challenges
Tutor
Allies and opponents
Talisman
Final test
The return

In addition to these structures, most plots can be boiled down to patterns:
The quest – Indiana Jones looking for the Ark of the Covenant
Revenge – Inigo Montoya in “The Princess Bride”
Love – choose any “chick flick”
Change – Scrooge in “A Christmas Carol”
Adventure – Dorothy in “Wizard of Oz” or Luke in “Star Wars”
The Chase – “The Fugitive”
One Against – Batman in “The Dark Knight” or Erin Brockovich
One Apart – Rick in “Casablanca” or Han in “Star Wars”
Power – Lord of the Rings
Death Overhanging – death can take three forms: physical, emotional, or professional. For physical, “Titanic”; emotional – “Inception”; professional – “Pretty Woman”

Sometimes it helps to have something in the ending reflect back to the beginning of the story. You can do this with an object or with a situation that mirrors one in the beginning. For instance, if you had a story about a blackout, you could have the hero flicking the light switch at the beginning and – nothing. He goes through the apartment searching for candles. The story continues and on the last page, he flicks on the light switch and gets light – then turns it off and lights a candle.

Or you could have the very nervous heroine entering a particular building and at the end, she enters that same building, but this time, everything has changed, especially her.

When checking on the plot line, ask yourself what is the hero/heroine’s goal? If he or she doesn’t reach the goal, so what? Why should the reader care? What makes the goal so important that we need to read? If the goal or conflict is too simple, you’ll end up with the reader saying “they could have done that on page one”, and if they could have, that’s not a good novel. If the goals aren’t important, neither is the story. Having your character take a shower merely because she wants to isn’t a compelling action. It only becomes important if she happens to be staying at a place called “The Bates Hotel”.

Once you’ve set the stakes, raise them. And raise them again. And again. Keep the story growing.

In a full length novel, you will probably have several sub-plots as well as the main plot. A sub-plot is similar to a plot, but may involve secondary characters. Even with other characters, they should have something to do with the plot, a link that ties them to the main story line. Like a plot, they must be tied up at the end.

Then go on to the following questions:
1. What is your story about?
2. Who are the main characters in your book? There should be one or two – three at the very most (hero, heroine, villain).
3. What do they want? What are their internal and external goals and are the goals important enough to carry the entire story?
4. Why does it matter if your characters do or don’t reach their goals? If it doesn’t matter, you don’t have a story.
5. When are the goals met? If too soon, you might have a short story, but not necessarily a novel.
6. How do they meet their goals? They should have to overcome obstacles that make it exceedingly difficult to reach their goals.
7. Do you have subplots? How do they relate to the main plot?
8. Is there enough of a story to fill an entire book?
9. What is the initiating event that sets off the rest of the action in the book?
10. Does the conflict escalate, with a major complication every few chapters, throughout the book? Is the conflict believable?
11. Do you use compelling hooks at the end of chapters to keep the reader interested?
12. Are there enough twists in the plot, especially towards the end, to keep the reader reading?
13. Do you have subplots? How do they relate to the main plot?
14. Are all conflicts, problems, loose ends solved at the end?
15. Do you have a compelling opening sentence? One that draws the reader in and makes him or her want to continue reading? If not, can you make it more compelling?
16. Where does the story start? Have you included too much backstory?
17. Do you have a catchy or unique title that is appropriate for the story?
18. What makes your story unique? What gives it an edge over other stories?