I often meet people who say they want to write a book or have been working on one for a long time. I say, “What are you waiting for? Why don’t you start (or finish)?” They hem and haw, “Well, blah blah blah, this or that excuse.”
If you’re not sure where to begin, write down your ideas. What genre do you want to write–mystery, romance, thriller, or __________? Familiarize yourself with the bestsellers in your market. Consider taking an online workshop, class, or reading a book or two about writing books. I recommend Dwight Swain’s Techniques of the Selling Writer and Debra Dixon’s GMC: Goal, Motivation, and Conflict.
Is there any research you need to do before writing–is your protagonist a cop, lawyer, wizard, knight, but you lack knowledge of job specifics? If so, make sure you don’t dwell too long on learning about writing and research and call that “writing.” That was a mistake I made when I first started…since I write medievals, I’d spend hours perusing books on the 15th century. It took hearing Catherine Coulter say in a speech at an RWA Conference that only new pages counted as writing to spark me to set weekly page/word count goals.
Make a list of next steps. Create a writing schedule and make appointments with yourself so you don’t keep putting it off.
I bet you’ll feel good about making progress, and might even be motivated to do more. Wanting something that’s in your control but not taking action can weigh on you.