First, you have to start and maintain a sharp hook. That means you have to have a sharpener. You have to have a fly that is so sharp that if he even picks it up, he can't expel it without the hook grabbing flesh. Next is the hard part. Lift like you are just lifting it off a rock.
Lets go back to the steelhead.
Your fly comes in, and brushes the rock. You lift it off, the steelhead sees the flies swims over and takes. Or, the fly comes in, the steelhead doesn't take the fly well, only plucks at it. You simply lift, which pulls away, now this prey is trying escape, and he body slams it. Or, he takes the fly softly but we take away.