Until I stumbled across this handy how-to page from Apple, I didn't realize I was accessing my saved drafts on the iOS Mail app in a wrong-headed, roundabout way. My method was to leave the All Inboxes screen and navigate up a level to the Mailboxes screen, where I would then tap one of my accounts in the Accounts section at the bottom and then select the Drafts option.
Because I am easily distracted, I often have half-written emails that I must return to. Thanks to Apple pointing out a better way, I can now access my saved drafts in the Mail app faster. And as an added bonus, the list of drafts accessed with this superior method is a combined list of drafts from all of your mail accounts.
Without further ado, I will share this superior method: tap and hold on the compose button. That's it! Just tap and hold on the compose button in the lower-right corner from the Mailboxes screen, the All inboxes screen, or any of your individual account inboxes, and you'll be able to access a list of all of your saved drafts from all of your accounts.
Now, there is one drawback. You can only tap to open your saved drafts from this list. Unlike when you access saved drafts from an individual account via the Accounts screen, there is no Edit button, which means you can't mark, move, or trash drafts using this shortcut. For quickly accessing a draft you intend to complete and send, however, it's a useful shortcut.
For more tips on the topic, I direct your attention to Five new features in Mail on iOS 7 you need to know.