• Aim for a variety of materials that will provide multiple perspectives on your topic.  For example, a history of the tuberculosis in the United States in the 1930s might make use of newspaper articles, an unpublished diary of a patient, a published book, a government document, and an article published in a medical journal at the time.
• Consult the notes and bibliographies of recently published, good historical monographs and relevant scholarly articles.  If much of the cited primary source material is located in a distant archive, you may need to rethink your approach to your research topic.
• Use the author search function in Primo.  You can use "corporate authors" to find writings published by government entities or businesses.
• For those of you working on topics related to American history, try searching the Digital Public Library of America, which continues to add digitized primary sources on almost a daily basis.  For 20th- or 21st-century topics, the Internet Archive can help you find media resources; it also offers the Wayback Machine which can help you find webpages that no longer are in existence.
• Need demographics? Try:

Books in Primo are assigned Library of Congress Subject Headings.  In many ways, subject headings are a form of tagging, in that they represent the content of the material and provide ways for you to efficiently locate more materials that are conceptually related. 

Library of Congress Subject Headings are also quite useful for discovering primary sources. The following subheadings usually are added to indicate that the material is a primary source: sources, personal narratives, correspondence, diaries, manuscripts, or notebooks.  Once you've discovered the subject heading for secondary sources, try adding one of the primary source subheadings to see what you find.  Here are some examples:

Secondary source subject heading:  Chinese Americans -- History.
Primary source subject heading:   Chinese Americans -- History -- Sources.

Secondary source subject heading: Women -- Europe -- History -- Middle Ages, 500-1500.
Primary source subject heading: Women -- Europe --  History -- Middle Ages, 500-1500 -- Sources.

Secondary source subject heading:  United States -- History -- Civil War, 1861-1865.
Primary source subject heading: United States -- History -- Civil War, 1861-1865 -- Personal narratives, Confederate.

Collins Library has purchased the American Antiquarian Society Historical Periodicals Collection!

Other recent primary source collections include the following:

A full guide to the collection is available here.