You can order some of the manuals from the PSIA web site
at the non-member prices (you might need to call vs ordering online). I would recommend the Core Concepts Manual, the Alpine Technical Manual and the Vail/Beaver Creek instructor handbook.
There is a lot of free information available on the National site and on some of the division web sites. The Eastern Division site has an exam study guide
that could easily double as a study guide for new instructors.
Other things you can do to get ready include brushing up on psychology & biomechanics, practice memorizing names of new acquaintances, practice listening skills, practice people watching/body language interpretation and practice smiling at people.
If you've never taught anything before, practice teaching something simple and familiar on a group of friends (e.g. juggling, how to kick a soccer ball, a stretch exercise). Do it in 10 minutes or less.
But please reailize that all of these activities (other than prior teaching experience) are overkill relative to what is expected of you as a prospective rookie instructor.
It's also possible that a resort near you is holding a spring hiring clinic. Call around, you may want to attend one even though you have no intent of working at that resort.
Finally, there are plenty of folks here to answer your questions.