It may be tempting to stun and fan the hammer. But if your aim is decent a one or two tap head shot is always better. Never stun fth a genji
Learn the impact arc of stun grenade. It will surprise you how its thrown. It's an absolutely trash ability in that it's poorly designed and doesn't do what you think it will half the time.
And above all else, dead eye is not a potg monster ability. You don't have to have 3 locks to fire it off. You're far better getting 5 player for 3/3 and having the rest of your team finish them than to have most of them take cover and take no damage. Oh and Learn which side of the screen deadeye first from first. You'd be surprised how often it's the difference between someone dieing to it or not.