In the absence of a narrator in Death of a Salesman, what devices does Miller use to provide exposition about character?

Flashback and hallucination are both used to provide
character exposition in the play, offering insights into the lives and characters of
Willy and Biff in particular. 

The flashback scenes help to
explore Willy's effect on Biff (for good and bad - mostly bad). They depict the ways
that Willy's arrogance passes on to Biff, almost as a form of moral instruction. They
also depict Willy's pride in Biff and his hopes for Biff's life. Finally, they explain
Biff's disillusionment and his break with Willy as a result of the discovery of Willy's
infidelity. 

Willy's hallucinations help to articulate his
ambitions and his vision of success. He imagines conversations with his brother Ben,
both reliving actual conversations and conducting new ones exploring ideas of failure,
suicide, pride and despair.