In all of the surveys done on aggressive driving, the behaviors that anger drivers the most are very consistent. When merging lanes, make sure you have plenty of room and always use proper turn signals. Don't drive slowly in the left lane. Avoid using the passing lane except for the brief time it takes to pass. Driving slowly in the left lane will frustrate other drivers.
Many drivers get angry when they are followed too closely.
Don't signal gestures to other drivers. Keep your hands on the wheel. Making an obscene gesture to another driver is sure to provoke him or her. Use your horn sparingly. Even a polite horn tap may be enough to provoke another driver.