If you are having trouble figuring out what your book is about and what your main characters' goals are, I have several suggestions to help you clarify your thoughts.
One is to write a description of your novel as I do when I write a novel blurb description for a query letter or the back cover copy of the novel.
In a short romance, I usually use two paragraphs to describe the book, longer or more complex books three to four paragraphs. If some important point fits one paragraph better than another, don't feel as if you must follow my structure. Put it where it fits. Interior and exterior conflict, especially, can be switched.
First and second paragraph: Introduce hero and heroine and give simple plot set up. What is the interior conflict of the novel? (What tears the hero and heroine apart emotionally?) Examples are from my unpublished novel, THE LORD OF THUNDER. Examples are bracketed.
KATE GRAEME, a professional landscape painter, has been hurt by a man who used her love to manipulate her, but she still retains her romantic ideals about love and marriage. MORGAN DESART, however, has turned his own emotional hurts into a coldly cynical attitude.
Enthralled with each other, Kate Graeme and Morgan Desart want a permanent relationship but can't agree on the ground rules. Kate seeks a loving romantic marriage, but Morgan demands a marriage of convenience with a prenuptial agreement. Neither will bend emotionally.
Third and Fourth paragraphs: What is the exterior conflict of the novel? What must both must achieve or defeat and what do they have to lose? This can include plot set up, place set up, the important secondary characters, and the villain.
When they become trapped alone together on Morgan's island estate for a week, open conflict erupts as they seek to convert each other to their own viewpoint. Morgan tries to entice her into a loveless marriage with his sexual mastery, but Kate resists this ploy and tempts him with romance and samples of a life together rich with love.
In this war of sexual desire versus emotional need, both know one of them will have to give in before the week is out because the magic between them is impossible to withstand.
If you'd like more examples or your book isn't a romance, read my article on writing back cover blurbs.
If your book is still pretty vague in your thoughts, I suggest you try the Bova method for firming up your characters and plot. Ben Bova's method is described in his THE CRAFT OF WRITING SCIENCE FICTION THAT SELLS. Yes, it's about science fiction, but it works with most popular genre fiction. (More on Ben Bova’s method.)
The Bova book explains the dynamics and interrelated nature of plot, character, conflict, and background.
The most important thing Bova explains is how character and plot interact with each other, and how character creates plot. (Plot as a characterization device.) He believes that the writer must examine her character and find his one glaring weakness and attack it through plot.
The protagonist should have a complex set of emotional problems where two opposing feelings are struggling with each other--Emotion A vs. Emotion B. (guilt vs. duty, pride vs. obedience, fear vs. responsibility, etc.)
This conflict should exist on many levels. In other words, the character’s emotional struggle should be mirrored in the action of the novel.
In classic STAR WARS, for example, Han Solo’s cynical selfishness wars with his unselfish love for idealistic Luke. Han’s ready to leave with his loot when the Alliance attacks the Death Star, but he risks everything to save Luke. That emotional conflict is mirrored in the struggle between the two political factions as well as in the thematic two sides of the movie--the good and dark sides of the Force.
Bova's ideas have proven useful to me, not only in creating my novels, but also as an aid when I'm stuck during a novel. When I can't decide where I'm going or have terminal writer's block, I reexamine my main characters’ Emotion A vs. B and realize where I've made a plot error so I'm able to start again in the right direction.
I hope these ideas can help you focus your book.