Create three sub-folders within your "inbox" folder; Reply, Follow-up, and Action.
As you come across e-mails that you need to reply to, move those to a "reply" folder.
As you come across e-mails that you need to follow-up on, move those to a "follow-up" folder.
Those e-mails requiring action, move to an "action" folder.
Delete, reply, follow-up, and action are your e-mail filters as you receive new messages.
Follow these steps and your e-mail in-box should remain "empty" at the end of each viewing.