"Do You Recognize These 10 Mental Blocks to Creative Thinking?" article by Brian Clark is fascinating, and you should read the whole thing, but here is a quick list at a glance:
1 - Trying to Find the "Right" Answer
2 - Logical Thinking
3 - Following Rules
4 - Being Practical
5 - Play is Not Work
6 - That's Not My Job
7 - Being a "Serious" Person
8 - Avoiding Ambiguity
9 - Being Wrong is Bad
10 - I'm Not Creative
If any of the above sound true to you, I also suggest reading "A Whack on the Side of the Head: How You Can Be More Creative" by Roger von Oech.
"To live a creative life, we must lose our fear of being wrong."
Joseph Chilton Pearce