The goal of the deck is to spam strangers to up your fire influence as high as possible, then finish off the opponent with Flash Fire. Flash fire can usually do 4-6 extra damage over a flame blast, plus it will only ever cost 5. Flame Blasts and Obliterates act as extra burn as well as potential removal. Grenadin acts as extra burn as well as a great spark enabler for Groundbreaker. Groundbreaker is just insane, and deals with lifeforce decks incredibly well.
As for the sideboard, extra Flame Blasts in case lighting storms or harsh rules make units ineffective. Rally and Swift stranger are for matchups where the burn feels ineffective. Soulfire Drake is a nice alternative to a couple of the Groundbreakers if the matchup isn't against life force or any other life matters deck. Finally Ruin, cause fuck chalice.