Here is the latest information on disaster preparedness from the United States Embassy - Tokyo.

"A major earthquake can hit the Tokyo Metropolitan area at any time.  With this in mind, we would like to remind everyone that emergency supplies should be readily available, frequently checked and maintained in good working condition.  We recommend that a three-day supply of food and water be stored in an area easily accessible within your residence.  Please check flashlights and other items that require batteries to ensure they are in working order.  Review your residential furnishings to lower the risk of injuries.  Heavy items stored at heights can cause safety issues during a quake.

Resources for earthquake preparedness, how to react and recover, can be found at the following sites:

http://tokyo.usembassy.gov/e/acs/tacs-7111.html

http://www.seikatubunka.metro.tokyo.jp

http://www.redcross.org/portal/site/en/menuitem.86f46a12f382290517a8f210b80f78a0/?vgnextoid=3750a5f0f013b110VgnVCM10000089f0870aRCRD&vgnextfmt=default

http://www.fema.gov/hazard/earthquake/index.shtm

http://www.ntt-east.co.jp/saigai_e/voice171/intro.html

For immediate information in the aftermath of a quake, it will be best to tune in to Japanese language radio stations.  Television stations may also be broadcasting depending upon the severity of the earthquake.  There will likely be some limited English information on major radio stations.  You may also try tuning in to the English language news broadcasts, but remember that the information will probably not be as current as the Japanese language information sources.
Before an Earthquake Occurs

Store the following items at work and home:
--    Flashlight and Batteries
--    Portable Radio
--    First Aid Kit
--    Water and Food Supply (enough for three days per person in household)
Emergency Procedures to Follow when Tremors Occur

(a)    First, stay calm.  Don't rush out of doors.  If you are in an underground passageway you are probably safer there than above ground.

(b)    Turn off all sources of fire and extinguish any flames.  In the event of a large fire, get out of the area.  Don't try to put out the fire yourself!
Get out!
(c)    Protect yourself from injury against falling furniture and objects.
--    Take refuge under a table or in a doorway.
--    Cover your head.
--     Stay away from brick and concrete block, fences, etc.
(d)    If you are driving a car:
--    Stop your car on the left side of the road.
--    Leave the center of the road open.
--    Leave the key in the car and do not lock doors.
--    Walk to the nearest evacuation site.  Any junior/high schools, hospitals or parks are considered emergency evacuation sites in Japan. 
(e)    Do not use elevators.  If you are in an elevator, stop it at the nearest floor and get off.
(f)    Listen to radio and television broadcasts.

Planning is the key.  Families should have enough supplies to last at least 72 hours.  It is important to discuss contingency plans with your family in the event you are separated as a result of an earthquake.  During an earthquake stay inside until you are sure it is safe and always keep in mind there is a good chance for aftershocks.  Practice with your families and members of household to ensure all know the path to the exit stairs, not elevators.

This message is to urge you to make a household emergency plan and work the plan with the entire household.  Also, visitors should be briefed on what to do in the event of an earthquake.  It's going to happen; it's just a matter of when."Source: http://tokyo.usembassy.gov/e/acs/tacs-7111.html