Deflection
Deflection forces a defender away from a piece, square, or line it must protect.
What to look for
Identify the defender holding the position together, then find a forcing move that makes it leave its duty.
Recognize the mechanism
Name the defensive duty first: a piece, mating square or line. Find a forcing action that makes the defender abandon that duty, and calculate what happens if it refuses the offered capture.
Common practical mistake
A sacrifice is not automatically a deflection. You must show which protection disappears and why the opponent cannot simply keep defending.
Training goal
Learn to attack the defender before attacking the target.