Holding the knife
Pinch the blade, curl the other hand, and the knife does the work while your fingers stay out of its way.
How
The usual mistake
Holding the handle like a hammer with the fingertips pointing at the blade — the cut wanders and the fingers are in its path; pinch, curl, and put a damp cloth under a board that slides.
Why it works
Pinching puts the hand where the balance is, so the blade goes where you look. Curled knuckles are a wall the flat of the blade rides along and the edge cannot reach.