Eat as healthy as you can. Take regular exercise, even if it's just a walk to shake loose the cobwebs. Get plenty of sleep. Rest if you get sick. Drink lots of water.
We all know we're supposed to do those things. But sometimes, when buried deep, deep inside a story, we forget everything else, resulting in what I refer to as a book hangover when the manuscript is complete. Write lots of books back-to-back with little to no time for recovery in between and it can have a knock-on effect, on both your creativity and your mental health.
Writers are notoriously bad at taking time off. Seedlings of stories are forever popping up inside our head, even if we're reading or watching a movie/TV or listening to music or out walking or socializing. So, technically speaking, even when sitting staring into space, we're still working. But we need that time and those ideas. It's called refilling the creative well.
Book promotion is not down time.
If you are Blogging, pimping your book on social media, scheduling posts, making Youtube videos, responding to comments, sending books out for review or offering a critique, you are still working. The same goes for reading books you intend to review or are judging for a competition. Add up all the time you spend doing those things and then add it to your writing time and you may suddenly discover you're working sixty to eighty hours a week! Keep in mind that even a forty hours per week day job will give you a minimum of three weeks vacation time per year, which I am certain you won't spend in the office, and you'll get where I am going here.
Down time is time spent away from work.
What we're talking about here is time with friends and family, an afternoon with your dog in a park, a night of dancing, a weekend away somewhere, a hobby that isn't writing related or a few days with the internet turned off so you can potter around doing mundane things which won't tax your mind (this would be the ideal time to organize that sock drawer). Think of your mind as a muscle. Even if you're a professional athlete, would you work that muscle twenty-four hours a day, seven days a week, for fifty two weeks of the year? Isn't it more likely you would rest it between bouts of training so it's competition ready? A little light exercise is fine. You can still scribble down any ideas that come to you during your down time. But you must take time off to refill that well.
Protect your mental health even more fiercely than your writing time.
Down time should be scheduled between books or around the holidays or for an actual vacation. Yes, there will be times when some things overlap. Line edits may come in, an editor may request a book early if another book drops out of a schedule, a particularly sticky story may take longer to write than you'd planned. You can't control those things. You simply have to deal with them as they happen. But you can control your deadlines, and be realistic both with yourself and an editor/agent about how much you can achieve in a year, including that precious down time. It's okay to say 'four books a year might be a bit much for me'. So long as you follow it up with something like 'I want to make sure I turn in the best possible books', an editor/agent will understand. Particularly if you're just starting out. If you're prolific and can write 10k per day you can probably manage more. That's entirely up to you. But don't skimp on the down time!
Don't risk burn out!
Take it from someone who knows. I was flying high, writing full time, and was regularly booked for talks and workshops and interviews. Then I stretched myself too far, worked myself into the ground, and hit a creative wall. Add that to family problems and a long bout of depression and I literally couldn't write. I produced three books in a decade as opposed to the three or four books I regularly wrote per year while doing everything else.
Creativity is a writer's most valuable commodity. Mental or physical exhaustion can stifle it. But the discipline required to sit down and write a book from beginning to end is worthless without it. So, be kind to yourself and make sure you schedule some serious down time!

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