Use a real throwing knife for practice, not a two-piece knife with a handle and blade. With a throwing knife, the weight is distributed evenly for flying through the air. The handle end should be dull.
Construct a large target to begin practice on. Make sure the knife can penetrate this target with even mediocre force, as it will take time to work up to throwing accurately at full force.
Assume a throwing stance for the easiest type of knife throw: where the thrower is standing still. Place your dominant foot in back and your supporting foot forward. Hold your throwing arm at a 45-degree angle in throwing position. Keep your heels in a line and strive for balance on the balls of your feet and through your core.
Throw the knife forward by extending your arm, flicking your wrist, and ending with both arms pointed forward toward the target after releasing.
Reduce the force of your wrist flick if the knife spins too much, making the dull end hit the target. Increase the strength of the flick if the knife does not fly with enough force to penetrate the target.
Throw at increasingly smaller targets. Increase the force with which you throw as you become more confident and accurate.
Eliminate spin if you continually hit the target with the dull end. Increase spin as you become more accurate.