When is the last time you had an original thought?
When is the last time you sat down in silence to just think?
When is the last time you thought through something, from the initial idea through to the logical end?
Thinking is hard, and thinking is work. A good way to improve your thinking, is writing. Writing forces you to develop, refine, and organize your thoughts. To get better at thinking, get better at writing; to get better at writing, write more often.