"Whatever your purpose, the best
remedy for fear of writing, any kind of writing, is the Knickerbocker Rule: ass to
chair.  If you’re afraid you can’t
write, the answer is to write. Every sentence you construct adds weight to the
balance pan.  If you’re afraid of
what other people will think of your efforts, don’t show them until you write
your way out of your fear. If writing a book is impossible, write a chapter. If
writing a chapter is impossible, write a page. If writing a page is impossible,
write a paragraph. If writing a paragraph is impossible, write a sentence. If
writing even a sentence is impossible, write a word and teach yourself
everything there is to know about that word and then write another, connected
word and see where their connection leads. A page a day is a book a year." 

– Richard Rhodes    from HOW TO WRITE: Advice and Reflections