The thing is, you really need to have a job before you arrive. Especially the type you are looking at doing. Sure, a lot of people can just show up and start teaching English as long as they have a degree of some sort because there are at any time schools looking for teachers. But it will be a little harder to find openings marketing and sales. And your competition will be a bit tougher since you will be competing with bilingual Japanese. And why would they bother hiring a foreigner when a qualified Japanese person can do the same job and, for a lack of a better way to say, be Japanese about doing it. Because there are a lot of things about working in a Japanese office environment that simply come natural to a Japanese person. So what you will have to do is find a job or position that is specifically needing a foreigner to fulfill it.
Join
International Creative Network - Asoboo and get their job mail. Keep a watchful eye on
Gaijinpot and any other non-teaching job sites you can find. It may take a while, but surely something will come around that suits you.