History isn't rote memorizations of dates and events--it is about people's lives at a particular point in time. Why is this important to a ghost hunter? You need to be able to separate fact from legend and history can give you that insight. You're looking for clues that will help you in understanding what may/may not have happened there. As DCMAG's Historian, I've found that my history background comes in handy.
Look at the architecture and location. Is it original? Renovated? On a major route? What style is it? Colonial? Victorian? Brand new? How was it constructed? These are major clues to help determine a time period. Even a brand-new home could have a haunting if something happened on the land itself. Most locations have changed hands at least once--even if it's within the same family. Sometimes you need to dig a little deeper. Check articles, deeds, wills, city and phone directories, maps, and surveys if you have to. These can give you a better idea of owners, the land, and events that may have occurred there. Sometimes the owners have a wealth of information, and other times might involve a little sleuthing on your part: whether online, at your local library, city organization, or historical society.
Sometimes you go into a location knowing some of its history already. Your job is to determine what's what and where things may have happened. Sometimes you will hit a dead end. It happens.