Isaac Asimov, the author of about 500 books, had an office in his Manhattan apartment that overlooked Central Park. This priceless view was completely blocked off so Dr. Asimov could focus on his job - writing.
On the other hand, Ray Bradbury's writing space was crammed with toys, magazines, posters, statues and photographs - all primed to inspire the next story or scene.
Preparing your writing space is a key to productive writing, but it depends on what your specific needs are. Most writers I know have problems with distractions, and should take a cue from Asimov. Limit the clutter. Limit the input. This does not necessarily mean you need to work in a monk's cell, but, if the things around you draw you away from the work, get them out of the way the day before. (Cleaning up before you write is an evil excuse to do something "productive" that is not writing.)
Of course, distractions do not need to be physical. The Internet, especially through social networks like Facebook, is probably the biggest killer of writing efforts on the planet today. Search beckons, chat windows appear. Email arrives with a distinctive chime. If this sucks you away from your writing, fight back. Close applications. Turn off the sound on your computer. Use a screen decluttering program. Or just detach your cable or shut off your wireless connection.
People can be distractions. I'll get into the dangers of husbandus interuptus or wifa interrupta or kidi interrupti in a later post, but the short answer to these is establishing boundaries. But, for many writers, the voices in their heads are the biggest distractions. Not the voices of characters, but the nagging voices that say laundry needs to be done, bills need to be paid, or the garden needs to be watered. All the tasks of career, family and household are important, but writing cannot fall the the bottom of a productive writer's list.
Making your reasons for writing explicit can move it up on the priority list. Write them down. Star, boldface and highlight the ones that are most important. Discuss them with your supporters (and avoid the deniers).
One teacher of mine, a successful novelist told me that her writing time was sacred. How sacred? She heard a scream one day, looked up once from her page and saw her son covered in blood. She almost left her writing desk, but, within a heartbeat, her understanding husband scooped up the child and drove away with him. She went back and finished her sentence.