Writing biographies is a difficult undertaking. It becomes virtually impossible when writing about a subject where there is nothing interesting to say about. The other extreme can be found when there is so much of the same to tell that it becomes repetitive. This happened to Peter Biskind.
Thousands of books have been written on how to become a freelance writer. Most of the publications are a total waste of paper or storage space. Some books are a waste of time but do no harm, but only a handful are worth reading. The Well-Fed Writer by Peter Bowerman is one advice book that might teach you some useful things. But as with all advice offered to you, be it personally or in any other form, you'll have to work it your way.