In James Joyce's novel Dedalus says:
"I will try to express myself in some mode of life or art as freely as I can and as wholly as I can, using for my defense the only arms I allow myself to use — silence, exile, and cunning.”
By silence I think he means being an observant being, a trait necessary to any artist, writer or poet. To witness in silence the mores and manners of society.
By exile I think he means being an unaffiliated outsider standing outside society. This is important to a writer because if you are a member of the establishment, church, or to a political party this may cloud your bias as you write. It probably means literally exile too because Joyce left Ireland.
By cunning I think he means to possess good craftsmanship, hard work and skill to impart new truths to humanity. Also, to be as cunning as Dedalus's namesake Daedalus of Greek and Roman mythology who makes wings to escape the labyrinth.
This observation of mine is incomplete and needs further development. Feel free to add your thoughts.