Introductory guide on using archives from the Society of American Archivists (16 pg. PDF). Contains sample finding aid.
Research at the National Archives
Learn what to expect when you research at the National Archives. This video addresses how to enter the National Archives building in Washington, DC, what security measures the National Archives uses, what you're allowed to bring into the research room, and how to use the records. Run time 2:12.
This list of online resources can be used as a starting point for your primary research.
The New York Times Historical Archive offers full page and article images with searchable full text back to the first issue. The collection includes digital reproductions providing access to every page from every available issue. Sept. 18, 1851 - 4 Years Ago, full-text.