R then Q your target at max range so you double hit the damage. Flash right before the Q lands and instantly AA W, then continue auto attacking.
AA then instantly W Q, AA and Flash to reposition so the Q hits your target on the way back. Continue to AA.
In longer trades AA then instantly W, AA again then Q instantly followed by more AA's.
For a quicker trade AA then instantly W to reset your AA and Q.
The most common trading tactic is to AA then Q as soon as the animation finishes, then AA again.
To trade from further away Q then AA, use W as quickly as you can after the AA finishes then continue to AA.