If you work better with soft music playing in the background, arrange to listen to your tunes while you complete your tasks.
If you're on the job, close your office door to deter people from stopping in to say, "Hi," or ask a quick question.
Close your door and turn off the phone.
If you have an important task at hand, it's important that you avoid unnecessary interruptions. Sitting alone can certainly help you to clear your head. Also, if you have Internet access, resist the urge to go online to time-wasting websites, like Twitter, Instagram, or Facebook.