The best way to get to a know resource before using it is to thumb through it. It's important to do this sort of proactive evaluation so that when you get a reference question you might have a better feel for the source, or type of source, most likely to answer that question.
Locate the following in print:
almanac
dictionary
encyclopedia
atlas
government source
Consider:
information at the front of the volume
how sections/chapters are organized
kind of information provided; depth
information at back of volume
how might your patrons use the resources