Accomplishments/events. One idea is to start and end with events that mirror each other in some way. Maybe you can start with a toy boat that the subject made when they were 5, and end off with a military submarine that they designed at age 55.
Turning points. What are the moments in the subject's life when their direction changed dramatically? The birth of a child? A near-death experience? Hitting rock bottom? It's the point at which a pattern changes; a new phase begins, progression become regression (or vice versa a cycle ends or a new ones starts.
Then consider what specifically you think would interest readers. Keep in mind that the most interesting questions may not be about what your subject did, but why. What obstacles did he face, and how did he work through the challenge?
What led to the subject's success or demise? Was there a certain passion (or obsession?) A particular relationship? A single incident of good or bad luck? A decision by the subject? Visualize witnessing what they witnessed. Imagine how they felt. Take pictures for the biography. If you can't visit the actual place, try to visit a place like it. Here are some ideas:3, where the person was born and died. Also account for regional differences. What's frowned upon in one place may be celebrated 30 miles (48 km) away. This can shed light on the subject's decisions, and their consequences. When researching the time period ask yourself: what were the social norms of that time? You can literally shape nonfiction. For a biography I make a rough chronology of the persons life, noting the high spots, low points, and other periods that are particularly interesting. Then I graph this and see where the peaks and troughs fall. Here is a process for deciding on a subject and giving your manuscript interest and shape. By Mary McVicker, published: October 29, 2011, is there someone youre interested in, someone whos been on your mind awhile, for whom theres no biography, either for yourself or for a younger reader?