From a personal viewpoint, I only say you're on the road to mastering a sleight when the sleight can be performed without looking at your own hands.
Any kind of body language or attention which is unduly paid to the sleight in a way which makes it look like you're contorted or unnatural is going to draw the spectator to that point.
Almost like changing gear in a car—next time you're driving, just take 2 minutes to realised you don't CONSCIOUSLY look at the gearknob, or even make any thoughts about using the clutch pedal. But both are done in synchronisity which is almost instinctual. Almost like breathing.
Of course, that last metaphor is wasted on anyone who doesn't drive or who uses an auto gearbox
