Plan to split your blurb into four specific sections. The first section establishes the main characters and setting of your novel. The second describes the conflict that makes up the narrative thrust. The third section escalates the conflict, giving readers incentive to purchase your book. The final paragraph outlines the questions readers can expect to have answered when they read your novel.
Establish the characters and setting in the first paragraph. Introduce your characters in a few concise words. Consider using adjectives that identify the traits and circumstances that make the people interesting. For example, the adjectives "orphan," "divorcee" or "widow" instantly communicate a character's life experiences with which readers might identify. The setting is also important, as many readers choose books with historical or geographical settings that are meaningful to them in some way.
In the second blurb paragraph, describe the conflict your characters will face. From romantic misadventures to a quest through a mystical land, conflict is the most important component of any successful novel. Readers are more likely to find your book concept compelling if they know that your characters have something significant at stake.
In the third section, escalate the conflict you established. A good novel often hinges on the idea that a situation usually worsens before it improves. The key to this paragraph is giving readers an irresistible fascination with your characters' situation that they can only resolve by reading the book.
In the final paragraph, highlight the questions readers might ask after learning about the conflict. How will the characters resolve their differences? How will they escape their particular situations? Repeat the circumstances that create conflict for your characters: "Now they're on the run from the authorities -- can they clear their name before time runs out?" or "She can't stand this handsome rogue, but is he the only man who can help her restore her family's name?" Provoke questions that potential readers know will only be answered by buying and reading your book.