Believing that biographers do need to have a sense of the history of the genre,
Asking yourself who, ultimately, will be interested in, or willing to read, the life you're recounting should be your constant concern. When biographies fail to spark interest, become tedious or unsatisfying, it is usually because the biographer had lost his commitment to engage the reader and is taking the audience for granted, by getting too self-absorbed in the life he is depicting. Never forget or neglect the reader!
We should all remember that.