From Matt Wiebe:
Stop. Read that again. The key to writing is writing. Just doing it. There’s no particular technique that will help you to be a better writer than just doing it. Write all you can. Read all you can. Move the cursor to the right. Make the clickety-clackety sound on your keyboard. When you don’t have anything to say, write about how you don’t have anything to say. When you have writer’s block, write about your writer’s block: its shape, texture and hue. And before you know it, you’re writing. Don’t question what comes out, like why I thought writer’s block has a hue.
While Matt’s talking about writing, you can apply this to most any creative endeavour. I always let myself get hung up the wrong thing instead of just doing the thing.