No matter what, keep your workspace comfortable and motivating! Have flowers near your desk, burn scented candles, have a cushion on your chair, whatever it takes to make you feel comfortable while working. Our surroundings really do make a difference!
To me, natural light is very important and so I always work near a window and wake up early enough every day to see the sunrise, even at weekends. I also make sure to go out for a walk at lunchtime everyday to get some fresh air and sunlight, no matter how little that might be during dark winter days.
Plants and flowers also calm me and so I always have both or either near my workspace. In particular when working from home, this is so important to me!
What helps you to concentrate and keep motivated while you work?