This article on Lifehacker deals with creativity in general, but I felt it could be applied to writing specifically:
I believe that creativity can be taught, and I know for a fact that I've become more creative over time. It's not about finding the ‘one' idea, but rather about using creativity to achieve everyday personal and professional goals. I use creative thinking to sell my product and ideas to people, design better, and even to overcome personal obstacles, going outside my comfort zone.
Iris Shoor breaks down her approach into these sections (expanded after the link):
- Changing one part of an idea at a time
- Don't start at the beginning
- Create a range of alternatives, from the standard to the extreme
- Get outside the box—into someone else's
Click through for the original: http://lifehacker.com/5940145/why-creativity-blocks-happen-and-how-to-overcome-them