Every writer's process is different. Some are what is called pantsers, where the writer doesn't plot out the story before hand but instead writes as the muse hits them and allows the plot to evolve as they write. Then there are the plotters, those writers who plot out every detail of the story before they ever set their fingers on the keyboard. There are some highly successful writer's in both camps so I don't think anyone can say one way is better than the other, just different.
When I first started out writing, I was a pantser all the way. I just wrote what came to mind or went in the direction the characters took me. Now, however, I tend to be more of a plotter. I like to have my road map to follow though there are still times when the characters take me on a bend in the road that I hadn't planned, but having my plotted road map handy helps me to bring the characters and the story back in line so I can move forward. Writing suspense requires more plotting and keeping track of all the details, but I still find my characters will surprise me occasionally and do something I hadn't expected, which makes the writing process fun.
Whether you're a pantser or a plotter, as along as the book gets done, you're okay.
So what are you?
A pantser? Or a plotter?