Creativity, I think, is a muscle. Use it often, and boldly, and it will grow. I'm a fan of 'doing every day' challenges, when you have a limited time frame and a work to produce, I think it switches off the critical part which demands perfection. Sometimes quantity is better than quality, I say.
So I particularly love this project, 365; make something every day, showcasing some of the projects chosen by participants. Some have subject themes (faces, two headed cats, self portraits, houses); some are focused on the technique (granny squares, drawing, beading, bookmaking, weaving, paper); and some do a bit of everything.
Don't take my word for it, go have a look. Lots of people make lots of interesting things.
And with that kind of quantity, you can pick and choose and build quality. Without the self confidence to run with an idea, any idea, it's impossible to make the leap into a perfect outcome. Make mistakes.