Creativity thrives when you don't stay stuck in the same old routine. Even the littlest changes can have good consequences for getting you out of a rut and encouraging creative thinking.
Get outside your comfort zone. Doing new things, especially things you haven't planned for helps you to cope more easily with new situations. It also helps to open your mind and introduce you to new ideas and situations which can help you come up with new or unusual ideas.
Be spontaneous. Do things that you haven't planned for, occasionally. This will force you to adapt to the moment and overcome problems on the fly. You could even tie this in with an ongoing project.
Change little things. For example: walk home from work a different way each day. Change up which coffee shop you go to in the mornings.