Some say that the best way to learn how to do something is by watching others. That can be a little tricky with routing and switching, but fortunately Cisco has published their own internal standards for IP addressing.
Cisco’s global network engineers have learned to make IP address planning a required part of planning any new service in order to manage the limited and sometimes inflexible resource of available IP address blocks. Public address space is conserved as much as possible, and private addresses are used in a variety of services whenever it makes sense.
Their best practices document (available online as a PDF) describes the Cisco IT standards for IP addressing, including how and where and why private and public addressing is used. It also describes some of the priorities and policies related to allocating address blocks within a network, and managing address resources within the enterprise.