I read, and reread the casebooks and rulebooks throughout the year, not just in preparation of the new season. I also practiced and revise my mechanics throughout the year. When the new rulebooks come out, I usually try to focus on wording/editoral/actual rule changes, and cross referencing between the various rule sets.
Of course, those of you who are familiar with the way we do softball here in Texas also know that our off season usually extends from a period somewhere in the middle of December until about the middle of January.