There is no better block-breaker, in my mind, than allowing oneself to be "shitty". I actually "won" NaNoWriMo writing some unpublishable tripe full of sex. Of course it had a somewhat coherent story to it, but one would have to dig too deep, so that it'd probably need a total rewrite. Though I haven't exactly kept my NaNoWriMo pace since the 25th of last November (sadly), I am growing slowly accustom to letting my "first drafts" be "first drafts", which makes writing them somewhat less difficult.