In a previous blog entry I wrote a series of tips regarding coming to Japan and learning to live here. I may accidentally repeat some of that advice this time, but I suggest that potential job seekers go back and read all the entries from July.
In essence, finding a job in Japan has gotten much harder since the 1990's. More foreigners have arrived with basic skill sets that increases the amount of competition you'll face for a given job, plus Japanese companies have gotten more picky about who'll they'll accept for a position. In addition, the economy has nose-dived again, so that at best you can expect only $40,000 (USD) per year for most non-management jobs. Most of these jobs also require JLPT (Japanese Language Proficiency Test) level 1 or 2, or JETRO's BJP (Business Japanese Proficiency) level 1 or 2. So, study for Japanese language proficiency before even thinking about getting a job here. Being "conversant in Japanese" doesn't cut it any more. Tech companies want proficiency certification. (And the Japanese government requires a university degree before you can get a work visa.)
Keep in mind that if you don't have a British, Canadian, New Zealand or Australian passport, you're going to be fighting an uphill battle. Those countries have an arrangement (called a working holiday visa) with Japan that allows those nationals to hold a job for 9 months (renewable up to 2 times or so) without needing a sponsored working visa. So, most Japanese companies will hire from working holiday visa holders first, since it's a real pain to fill out the paperwork to sponsor someone for a working visa. This means that if you're from the U.S., you either need to marry a Japanese national, or find a company to sponsor you. It really is becoming more important to join a company based in your home country and get them to station you in Japan, if at all possible. Some international companies, like Tokyo Electron, have Japanese job openings listed on their websites. Or, join the military and get stationed here as part of your service.
English teaching used to be a big opportunity for U.S. citizens, since U.S. English was highly prized in the 1990s. However, the switch has been to British English (mainly because of the visa issue). Also, one of the biggest English schools in Japan - Nova - was discovered to be horribly mismanaged and went into bankruptcy and it's upper management faced criminal fraud charges. Since then, student attendance at the other schools has dropped, and the best wage you can expect is about $28,000 annually (just above the poverty level). The schools still do offer visa sponsorship, but the preference is again for working holiday visa people. There are many openings for English teachers in elementary, junior high and senior high schools, but those positions usually require some prior teaching experience and certification (either as an ESL (English as a second language) instructor, or one of the other certifications). It is possible, too, to advertise yourself as a private English teacher for one-on-one lessons, but unless you have a working visa already and are trying to teach on the side, you'll probably be able to work as a private language teacher only if you have a spouse visa.
More in detail later.