This Stanford University study (from 2014) finds taking a walk is a surefire way to be more creative:
The overwhelming majority of the participants in these three experiments were more creative while walking than sitting, the study found. In one of those experiments, participants were tested indoors – first while sitting, then while walking on a treadmill. The creative output increased by an average of 60 percent when the person was walking, according to the study.
I agree with this study. Walking does get my creative juices flowing…
However, I find driving my car (with the radio off) exponentially boosts my creative flow.