If you ask anyone with recruiting experience how to proceed with a job hunt in Japan, they'll probably suggest all of the following - register with the recruiter agencies, register with the online job sites, and network, network, network. In any case, don't slack off on doing the job hunting yourself, because requests for interviews aren't going to just fall in your lap.
Networking is a really big issue in Japan. Japanese people aren't going to trust someone that they just meet cold. Instead, they'll be much more receptive to someone that is recommended to them by someone they trust. So, you want to go to parties, attend industry meetings and events, and otherwise just keep yourself visible. Don't push too hard - you'll create the wrong impression if it looks like you're just using someone for making contacts. In essence, look at it as having a large circle of friends that help each other out. The more real friends you have, the more likely that they'll suggest your name to a co-worker or boss when an opening pops up. Remember though that this will take time, so be patient and make sure that you have a financial reserve that you can fall back on as needed.
Having said this, there aren't that many networking opportunities. Maybe events at the U.S. or Canadian embassies, a couple of cycling and outdoors groups that get together occasionally, and one group that shares an occasional monthly "British tea" gathering. Being fluent in Japanese may result in your learning about other industry events that aren't advertised in English magazines, which gives you another reason for getting certified for Japanese proficiency (JLPT level 1 or 2) before coming here.
MAKE SURE YOU BRING MEISHI!!!!!
"meishi" is the Japanese name for business cards. These are your life blood when networking. Always have 10 or 20 cards on you where ever you go. Treat the other person's card with respect, reading it carefully to understand their job function and company they work at, since this is crucial in determining how they will treat you and how they expect you to treat them (watch them for examples for how to treat the cards). You can get meishi printed up at certain office supply stores or online. You can also get cheap, decent-quality card holders from one of the many 100 Yen Shops in town. On the meishi, at least include your name, phone number, address and e-mail address. You may want to include your webpage URL if it has work-related info on it. Definitely include your company name and job title if you have one. Try to have the card in English on one side and Japanese on the other, if possible.