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.
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.
Oliver Wendell Holmes Library Catalog
When searching for primary source at the OWHL be sure to add the phrase "primary source" to your search. For example if you are looking for primary sources for Thomas Jefferson, your search would look like this: "Thomas Jefferson" and "primary source"