This one can be a bit tricky. If you go for headshots it will be a bit harder to get this. Headshots are often 1 hit kill. This means if you shoot and miss then shoot again and kill the enemy you will have a 50% accuracy. On the other hand if you shoot once and miss, then shoot an enemy 9 times in the leg to kill him. Your accuracy will be 90%. So to cut to the point, get multiple body shots instead of a single headshot as this will be the best way to increase your percentage. The more bullets you shoot on target, the less damage a single miss will do to your total.
Complete game with 70% or higher shot accuracy