I stumbled across this bit of writing advice last year and it's one that I loved immediately and it's also one piece of advice from the many I've read that's stayed with me.
So I thought I'd pass it on...
One of the few things I know about writing is this: spend it all, shoot it, play it, lose it, all, right away, every time. Do not hoard what seems good for a later place in the book, or for another book; give it, give it all, give it now. ...Something more will arise for later, something better. These things fill from behind, from beneath, like well water. Similarly the impulse to keep to yourself what you have learned is not only shameful, it is destructive. Anything you do not give freely and abundantly becomes lost to you. You open your safe and find ashes.
-- Annie Dillard from The Writing Life