As I mentioned in a previous tip, there's a very simple way to access drafts you've started on your iOS device—just press and hold on the Compose button in the Mail app.
But in iOS 6, this feature has become much, much better. Before, you could only bring back your last saved draft like that, but now it'll show you a list of all of your drafts, no matter what account you created them in.
From that screen, just tap one to continue editing it. You can also swipe across any draft to bring up a Delete button, which'll get rid of it forever and ever and ever.
I would install iOS 6 a thousand times just for this one feature. OK, so that's hyperbole, but it's still pretty nifty.