[I]t's almost impossible to get any real thinking done at work. Not just because of interruptions, but almost more importantly, the whole psychological and physical environment in which managers work tends to discourage contemplation and encourage activity. The higher the level in an organization, the more critical is the role of reflection and the less important that of activity, but so often we've become conditioned on the way up through the organizational ranks. How many bosses would give a word of encouragement to a subordinate if they were to come upon him sitting at his desk, chair tipped back, foot resting on an open drawer, and staring into space with an abstract expression on his face? They'd be far more likely to ask him what the hell he's doing, and if the unfortunate replied, "Thinking," he'd probably be advised to stop thinking and get back to work.
I'd also like to recommend this article on implementing creative though in the workplace.
Finally, I'd like to quote the following from Jack Foster's book, How to Get Ideas:
It is the child in you who is creative, not the adult. The adult in you wears a belt and suspenders and looks both ways before crossing the street. The child in you goes barefoot and plays in the street.