Put a stop to interruptions.

Be inaccessible
 - Work from where people can't find you. 
 - If you are in an office, have a CLOSED DOOR POLICY.

Don’t answer the phone.
 - Turn off your mobile phone. 
 - Give your receptionist an updated "VIP list" of calls you don't want to miss.
 - Support them 100%. They should have confidence when screening.

Deal with fax and email.
 - Train others to communicate with you via fax.
 - Have your staff sort faxes out in order of urgency and only forward the important ones to you.
 - After lunch, take an hour to look at morning faxes, e-mails, and calls.
 - Deal ONLY with the urgent ones. 
 - Take the last hour of the day to look at the afternoon's accumulation.

Set the timer on the bomb.
 - If you take a phone call, set up an exit time.
Example: "Tom, I have XXX starting in 15 min, but I wanted to take your call - I hope that will be enough time for our discussion. Do you agree - or should we set up another telephone appointment?"
- Do the same with drop-in visitors.