Inbox Zero is email bliss. Having an empty Inbox has a very calming effect. Not to mention that email is a terrible system to manage your to-do list.
With each email in your Inbox, touch it only once. If you can delete it, just delete it. If it needs to be archived, archive it. If it requires action and you can action the email in less than 2 minutes, then action it, and archive it. If it requires action and it will take more than 2 minutes, then create a task in your to-do manager and file the email in the waiting folder until you can get to it.
Those endless chains of emails that cc everyone and their dog are a total waste of time. If an email was not addressed to you, then it doesn't require your immediate attention. Create a mail filter rule to move any emails that don't have you in the TO line, to a separate folder that you can scan once in a while at your convenience.
How many times do we lose concentration when our attention is interrupted by totally unimportant emails like Facebook notifications? Unsubscribe from as many as possible, and for those that you really think are important, create a mail filter rule to move them to a separate folder that you can scan once in a while at your convenience.
Unsubscribe from all newsletters that are not important and get a decent Spam filter. If you can't unsubscribe, create a mail filter rule to blacklist those senders so you don't get those emails anymore. The less time you waste on unimportant junk, the more time you'll have for important things.
Email is one of the most intrusive blights of our time. When you need to concentrate on important things for a stretch of time, turn your email off. It takes many minutes to recover from a few seconds of email distraction, so get rid of the distraction when it will hinder important things.