Head shots are a key component for sniping. It lets an opponent know that you are capable of causing a greater interruption to their plans, and can do it at will. The only way to consistently get headshots is through practice. Start off aiming for body shots, and then as you learn to hit a target, refine your aim for head shots. Run the Sniper Drills listed here, and your accuracy and confidence will quickly go up.
Shot shaping is the most refined art of sniping in a FPS. If you hit someone in the back of the head, they make a very distinctive tumble as they fall. It is easy to spot where the shot came from. When you are behind lines, before they know where you are, shape your shots to mislead them. A shot to the back of the knee makes them fall back, as if they were hit in the front of the chest. A shot to the side of the knee will make them fall down, as if they were hit in the side of chest. If you learn to apply two skills Calling the Shot, where you know who you are going to hit, and shot shaping, you can easily have 3-4 people looking for you in 3-4 different directions, and none of them looking at where you actually are. They will communicate with each other to locate you, and will do nothing but confuse themselves.