Tracing ancestors and descendants is by far the most popular research method. Researching ancestors means you work back in time from a given person. Researching descendants means you work forward in time from a given person. You will soon discover that working backward and working forward are both needed.
Start with yourself and go back in time, tracing your ancestors from generation to generation by compiling names and the dates of births, marriages and deaths found in various information sources. Your object is to trace your family's history as far back as possible. The most helpful sources for doing this are birth, marriage and death records, immigration, citizenship, census and military records, and records of land rental or ownership (See What to Search: Topics).
This method can take two approaches:
Unless you are documenting only direct-line ancestors (your father and mother, and all earlier fathers and mothers), you will also record aunts and uncles and cousins, and their marriages and children. Finding the children of aunts and uncles and cousins means you will be working forward in time toward the present.
Do not neglect to go "sideways" if you get stuck. Often, researching more about a spouse or sibling of an ancestor will provide clues that lead you to more information about that ancestor.
To find details on the lives of your ancestors, you will comb through the records mentioned above plus other sources, such as notarial records, wills, deeds of land sales, newspapers, city directories, and so forth. You will also learn more about how your ancestors lived by studying the historical and cultural milieu. This will help you build a more complete picture of what their lives must have been like.