For me, the most important thing is the overwhelming desire to write about a particular figure. That usually means I already have--even if I can't articulate it yet--a vision of my subject. I have already decided I'm right for the biography. Everything else, then, will have to fall in line, no matter what obstacles I encounter. To prospective biographers I recommend that you know yourself first, that you know why you want to write about so-and-so. When you have convinced yourself--or as I like to say, deluded yourself--that you are the best person for the job, then it is time to take on all the other troubles you will surely face.