I've always been fascinated by the rituals writers have and the different methods used for getting 'in the zone'. Maya Angelou said (in a Paris Review interview) that she wrote in a hotel room with a glass of sherry to hand, Hemingway worked standing up, while George Orwell, Mark Twain and Marian Keyes are known to prefer writing in bed.
Some writers like the hustle and bustle of a busy cafe, others need complete solitude and silence. While plenty of writers don't like any music while they work, others rely on classical music or film scores to put them in the mood. Stephen King, perhaps unsurprisingly, listens almost exclusively to very loud rock and metal.
It's important to work out the rituals and habits that suit you best as a writer (and, equally, not to let the absence of your 'ideal' working conditions stop you from writing regularly) but it's also good to try new methods every now and then, which leads me to soundtracks.
Even if you don't think you like listening to music while you work, hear me out... Making a soundtrack for your book can unlock your story in unexpected ways; it can provide insight into character and inspire the tone. Better still, if you listen to your soundtrack every time you work on your book, it'll become a shortcut to that world, and putting it on after a break (perhaps in between drafts) can help you find your way back into the story.
Making a soundtrack is an intuitive process. The idea is that you pick tracks that 'feel right' for your book. If you're at the very beginning of a project, choosing music can help clarify the mood you're aiming for and, of course, you can alter or add to it as you progress.
You can make a soundtrack that conveys an overall mood for your book, or you can include songs that are connected to specific characters or moments.
I avoid music that already has personal connotations, so have to do a bit of searching to make a soundtrack. This is actually a brilliant part of the process because it makes me think about my characters and story in a new way, and when I hear something that 'fits' it lights my mind on fire.
If I know of a film or television series that has a similar feel to the story I'm writing, I look up the soundtrack and see if there is anything suitable I can use. I search YouTube with key words, use Spotify and ask friends for recommendations.