How can you help if you are already in Japan?
The following website gives lot of information on how can you help and what you should or should not do if you are in Japan.
http://www.timeout.jp/en/tokyo/feature/2532/japan-earthquake-how-you-can-help
Summarizing some options:
1 - What not to do: Don’t travel away from your home area, if you want to physically help. Remain where your home is, in order prevent overcrowding the public transports/roads.
2 - One of the options for helping is to donate blood, give blood is one of the best and easiest things you can do. The necessity for blood donation/usage tends to increase drastically as victims are being rescued.
3 - If you feel like donating money, the following web-site (in Japanese) will help you to find where to transfer your donation to: http://cause-action.jp/
4 - One thing you must do: Save electrical power! Problems with some of the power plants are keeping them of operating normally!
Over usage of the currently available electrical power may lead to power outages (blackouts) in certain areas, which will lead to further difficulties in the rescuing operations and medical treatment of victims.
Use electronics and house appliances as minimum as possible, turn off lights, don’t use elevators, avoid using heated water… small things like this will help.