I really enjoy watching the series Who Do You Think You Are? Basically, celebrities go on a journey to trace their ancestors and usually find interesting relatives in their past. As I was watching an episode yesterday, it occurred to me that I was watching a lot of backstory. And the backstory was interesting.
What made the celebrity's backstory interesting to watch and how can we apply it to our writing?
(1) If we love the celebrity, we want to learn everything about them, including their history. What does that mean for writers? Well, if our readers love our characters, they'll be more willing to find out about their past.
(2) Not everything is revealed. I'm sure the amount of information uncovered during the celebrity's journey is immense. The viewer doesn't get all that information. Often what is released is how the ancestor's career choices or family situation matches the celebrity's. What does that mean for the writer? Make the backstory relevant. Only release backstory relevant to the character and the story.
(3) The celebrity travels a lot, and we see their reactions. We are taken to the places the ancestor's lived. We see their houses, their workplaces, their art. Then we see the celebrity's reaction to the revelations. Writers can do the same thing, we can add backstory, but make sure you break it up with present day reactions. 
How do you add backstory?