It can be hard to get motivated when you need to write but aren't feeling up to it. Here are a few things I do to keep it going:
Exercise: Although it sounds counter-intuitive, getting up and moving can be a great way to get your brain moving. Physical movement helps the brain to stay sharper, longer, and gives you some time for your mind to wander. There have been studies displaying the "tremendous benefit of aerobic exercise on a person’s memory and demonstrates that aerobic exercise can reduce both the biological and cognitive consequences of aging.” These studies have demonstrated that increased blood flow to your body also increases blood flow to your brain, boosting your brain power and keeping your brain from aging prematurely. This can help to bolster your ideas and your writing power.
Reading: As a writer of any genre, you should be reading and studying your genre for at least an hour a day (for full-timers, at least). So if your brain isn't in a writing mood, you can help to get there by reading in the genre in which you are trying to write. Have some articles on gardening due soon? Read a blog on gardening that is highly regarded. Trying your hand at epic fantasy? Look at the highest rated epic fantasy books on Amazon, Barnes and Nobel's website, or even walk into your favor bookstore and ask for a recommendation.
Meditate: If your brain is feeling a little overworked from a long day at the office or running after the kids, it may be difficult to get writing. Relax your brain and give it a break with a little bit of meditation. There are so many videos and books out there that are dying to help you learn to meditate. And there are hundreds of videos about the benefits of meditation as well. So give your mind a mini vacation and relax, breathe, and just let a little bit of time pass you by.
Coffee: I'm pretty sure coffee has a placebo effect on my writing, but a little jolt of caffeine seems to make writing a little easier. Maybe you just need a boost from a little sugar, a spot of tea, or to pop a few vitamins to get you back in the groove.
Take a break: If all else fails, just walk away from it. Writing can be stressful, time-consuming and very difficult at times, and flow easily from your fingertips at others. Maybe all you need is a little break from writing. So take a few hours off and do something you love, so you can get back to the things you love to write!