The New Yorker’s Daniel Mendelsohn called memoir 'the black sheep of the literary family', riddled with self-exposure and the airing of personal laundry. So what are the rules for writing about one’s life. The authors of some extraordinary and varied works – Brentley Frazer (Scoundrel Days), Graeme Innes (Finding a Way) and Kim Mahood (Position Doubtful) – tell Catherine Eccles about their approach to this revealing form of writing.