When you let your conscious mind take a break from a task, your subconscious mind continues to process the information in the background. Sometimes, insightful ideas will flash into your mind. To encourage this, you can try this exercise.
Sit down and write a letter to yourself about the problem you are working on. Pretend that you are writing the letter to someone who knows nothing about the project; give a good description, including everything that you have done to date. Be as detailed as possible. Don’t forget to mention any constraints that are imposed on the problem and what types of solutions are preferred. Then, give your subconscious a deadline. For example, you could write, “I expect a full report by the end of the week!” It may seem silly to write to yourself in this way, but give it a try. Now close up the letter and put it away.
Unbeknownst to you, your subconscious will continue to think about the problem. When the deadline approaches, open up the letter and read it. Chances are that by that point (or possibly earlier) you will have experienced a flash of insight that illuminates a potential solution.