Four things the Spear Throw demands:
Accuracy
Coordination
Power
Timing
Cross body throwing, resulting in a lack of power.
One of the first things we teach athletes to improve in their throwing is to use the non-throwing hand for aim. Keep it outstretched and pointing at the target. When practicing, start without the spear and move your throwing hand from your ear to your aiming hand. You should end up making a triangle with your hands and shoulders. Try to notice how much your hips rotate or if your balance shifts.
Most people we see at the races try to throw the spear like a baseball. This usually kicks out their rear leg behind them and gets their center of balance moving forward in front of their body. The power for the Spear Throw should come from the body like a good punch or a dart throw. Push through your rear leg, aim slightly above the target's center and throw forward powerfully in a straight line. Keep your chest and eyes facing the target.
Accuracy can be highly dependent on heart rate and state of mind. We try to coach our athletes to slow down and breath before the spear throw. Do not rush into it. Take your time, inspect the equipment. Find a lane where the spear has already successfully hit the target. Visualise making a successful throw. Keep your eye on the center of the target. Throw powerful and straight.