ALWAYS use the date range feature when searching for primary source newspaper articles. An article is only a primary source if it was published at the time in which an event took place.
Always do reading in secondary sources before looking for primary sources. Often times, information in secondary sources will lead you to a primary source. For example, an article in a reference book might reference a speech or letter written by the person you are researching.
Oliver Wendell Holmes Library Catalog
Do a keyword search for your topic and include the words primary source in your search string. For example: when looking for primary sources about Thomas Jefferson you should type Thomas Jefferson primary source into the search box.