Knowing when [what dates or period] to search for a particular event for a person is just as important as knowing where to search.  By making a simple timeline of when the person appears in a record group can narrow down the search of the next event.

For example, if I know that a father was a witness to his son’s marriage in 1847, but was listed as deceased on his daughter’s marriage certificate in 1851, the time span is narrowed to a five year window.

Another great thing to add to a timeline is a listing of world, regional, and local events occurring at the time being researched.  I have troubles keeping all the wars and historical events straight, so by using a timeline, I can better calculate why a particular person might not be where I thought they should be.

In The Source: A Guidebook of American Genealogy by Loretto Dennis Szucs, timelines and other first steps are explained in great details.