i agree with some of the recommendations already posted here, but i also highly recommend a technique known as 'freewriting.' it's based on the concept that ideas aren't endpoints, they're stepping stones to other ideas. the more ideas you have, regardless of quality, the better chance you'll navigate to a really good idea. i saw a review here on HN of an excellent book called Accidental Genius. here's the link to the review:
http://www.dextronet.com/blog/2011/07/accidental-genius-summ...