I've always loved reading thrillers . . . so it was only natural that I wanted to write thrillers. I've often heard its the beginning that is the hardest - lets face it ... a thriller should start out with a chill!
Step 1. Choose the idea that defines your book. It isn't your plot, character or your hook. It's the main 'idea' or 'theme' ... such as the earthquake, the pattern of the serial killer, or maybe it's the deadly virus.
Step 2. Ask the What-If question. I've often heard this described essentially as your elevator pitch—that sharp, well-put, snappy description of your book you should have at the ready should you be stuck in an elevator with an agent or editor. the rule - two sentences and not more than 25 words. Make it as tight as possible, and don't include characters or plot twists. It's worth spending days creating those two sentences.
One What-If example from my work: What if every murder she writes about in her novel is now happening for real?
Step 3. Answer the What-If question. The answer to this pivotal question is the reason people think they’re reading the book. The fact is —people read to the end of a book for the characters. But you still need something to keep them flipping pages. Your plot or theme is simply that tool that makes the reader stay with the characters.
Once you have the answer to your What-If, you should focus solely on the characters of your book, or it will be plot-heavy and bog down. You'll risk losing your reader.
Step 4. Who are you going to write about? Look for the character who’s got the most at stake - the most to lose in other words. This is your main character - the most interesting and one you can weave your story around.
Step 5. Write it. Let's fact it ... once you're at this point - that story isn't going to stop bothering you until you sit down and write it! Your character haunts you nights and days .., taking you in directions you never thought of going. Make your character work hard - keep throwing him/her under the bus, locked in a basement, lost in the forest . . . so your character has to figure out how to survive the plot.