Buy an ATM call and an ATM put on the same underlying, same expiry, simultaneously. The straddle profits when the underlying makes a large move in either direction — beyond the upper or lower breakeven. Ideal setup: buy the straddle 1-3 days before earnings when IV is starting to rise but has not yet spiked to its peak, and close the position shortly after the announcement once the move has occurred and IV begins collapsing.