How Would You Document Your Job?

Q3vi1 asks: "As an support technician, there are several things I've learned about the environment I work in that would be difficult to find out without hours of research. Now I'm going to be moving and that means getting a new job. Before I do, I'd like to leave behind some of this information for the person who will replace me. How does one document all the details in an efficient manner for the next tech?"