David Allen's threefold nature of work:

• Pre-defined work: Work you've set up ahead of time.
• Work as it appears: Work that interrupts you.
• Defining work: You sit down and think about what work you need to be doing.

• Do It
• Drop it
• Delegate it
• Defer it

Only do it if it's going to take a minute and it's been scheduled. Otherwise, just drop it, delegate it and defer it.

• Change the way emails appear in your inbox: set up a folder for emails that you're Cc'd on and a folder for emails that come directly to you.
• Don't reply to emails in the morning (or at night): it teaches people that they should expect future replies from you at that time. 
• Keep your emails to 3-4 sentences.

If anything important happens in the world, it will come your way many times. 

There's no need to hit refresh every 5 minutes on news sites. Somebody will tell you. 

When you're multitasking you are actually doing something called task-switching, which requires context switching. And this harms your productivity overall.