Search newspapers using proper nouns for best results: names and places work better than themes and ideas. How would your theme or idea be represented as facts in a newspaper? What events would exemplify your theme?
If you can find dates or date ranges (using secondary sources), your newspaper searching and browsing will be much easier. In fact, the more pre-research you can do, the better.
Consider the stakeholders in the events you're researching. Historic newspapers rarely represent minority views.
Want feelings or opinions? Look for editorials and letters to the editor.
Pay attention to advertisements, classifieds, and business and shipping sections, not just news. Many newspapers even had legal sections documenting business sales, execution of wills, real estate transactins and more.
British Columbia Historic NewspapersThe BC Historical Newspapers project features digitized versions of historical papers from around the province. The titles, which range from the Abbotsford Post to the Phoenix Pioneer, date from 1865 to 1989.
Early Victoria NewspapersProvides access to four indices tens of thousands of summarized transcripts of article first appearing in newspapers published on Vancouver Island between 1859 and 1921: British Colonist (also called the Daily Colonist) from 1858-1921; stories related to the west coast of Vancouver Island; stories related to the Boer War; stories related to buildings, builders, etc.