Tip: Start by taking 20 minutes, two days a week, during your lunch break to take a stroll and daydream. Think about anything you want besides work — a beach vacation, building your dream house, playing shortstop for the Yankees, whatever. Ramp it up to three or four days a week. The next time someone catches you daydreaming on the job and asks you why you’re not working, tell them that in fact you’re tapping into your creative brain.
Try the above tip. It works.
Here's a useful process which works for me, and for my writing students.
Before your walk, write down a question. The question can be a writing problem, or any other problem.
Walk, but don't think about the question. Allow your mind to roam wherever it wants to go.
After your walk. Read your question, and write the answer.
You'll be surprised at the results.