Write everything down. Don't edit as you listen, you might miss a crucial piece of information. Over the years memories fade and alter. The stories people tell most often have a grain of truth in them. There are many clues right in your own home or in the attics of your relatives.
Bible records are an especially important source of information.
They were usually, but not always, entered at the time of the event. Any kind of record or memento that puts your ancestor somewhere in time and place. Even these can contain human errors. Primary sources are birth, baptismal, death and marriage records. Secondary sources provide you with clues to researching your lineage.