How can irony be effectively used in casually comic writing?

Irony is a key ingredient. 'Casually comic' writers often employ dramatic irony (where the reader knows something the character doesn't) or situational irony (where the outcome is the opposite of what's expected). Irony is typically subtle, not blatant, and relies on the reader picking up on the discrepancy between what is said or appears and what is actually meant or happens. It allows for a layered comedic effect.