Go when you are poor. It is very easy when you have only one suitcase. My story summed up:
Graduated university in December. Moved to Japan in January. The only preparation I did was arranged to live w/ a friend for a while. Got there, got a job, partied my *** off for the first year or so. Eventually settled down and got a real job.
I majored in Japanese so the transition was relatively easy, other than sharing a room, and getting acclamated to the cold weather (I'm from Texas).
EDIT:
Despite having a very pleasing college experience, and making almost zero money for a lot of work, my first two years in Japan was by far the funnest time of my life.