Always cite your sources. Follow these Quick Style Guides or the complete style manuals.
Quick Style Guides
Are you working with government publications? You may want to consult A Guide to Citing U.S. Government Publications developed by the Government Information, Maps and Microforms Services Department (GIMSS).
Full Style Manuals
Most citation questions can be answered with the quick guides above. For more specific questions, refer to these full manuals, or consult a librarian.