When the questions begin, listen to the entire question before answering. Don't think you know the answer and interrupt the questioner prior to him finishing the question, because you may guess incorrectly and you will also appear rude. Chances are you will only have to wait a few seconds before the rater finishes his question, and then you can proceed to give your answer. When you answer the question, be sure to look at each rater. Look them in the eyes when you talk to them. Do not let your eyes wander or dart around the room; this gives the impression that you are unsure of yourself or do not know the answer. Start with the person who asked the question, and then rotate to each of the other raters. Do this in a flowing motion so as not to look robotic. When you speak, be sure to project your voice so the raters will not have to strain to hear you; but on the other hand, don't shout. Your mouth may be dry; if they offer you water, use it. It is placed there for your use, and it won't be marked against you. If you can draw on other answers you have given when answering the current question, it will look as though you can pull together different kinds of information and organize it in a meaningful manner.
When you first begin to talk, your voice may quiver due to nerves. Don't let this bother you; just overcome it. Clear your throat, take a deep breath, and continue speaking. Don't tell the panel that you are nervous; they understand this because they have been in your position several times. When you begin to answer their questions, keep your hands away from your mouth so as not to block your answers. Also make sure you don't do anything to distract the panel, such as tugging at your ear, pulling strands of your hair and winding them around your fingers or cleaning your fingernails while you are answering their questions.
Remember, you are not writing a report, so don't answer in the form of a report. When you are asked a question, respond in a clear smooth cadence such as you would experience in a regular conversation. Don't chop it up with "cop slang" or sound like you're testifying in court. For example, if you are given a hypothetical situation where you are in charge, and a disturbance occurred, don't use the following terminology to answer the question: "After receiving a call of a P.C. 415, I responded to the location in question and immediately made contact with the victim and necessary witnesses. I put out an APB and then deployed my personnel to circulate through the neighborhood in an attempt to locate the perp and other individuals who may have witnessed the incident."
As you can see, this type of answer does not flow and makes you sound very stiff. Tell the raters exactly what you would do at the scene. Explain that upon arrival you would evaluate the situation, use your available manpower effectively to contact witnesses, maintain a perimeter to contain the area and attempt to locate and arrest the suspect or whatever else you felt would be necessary to complete the scenario. My point here is to keep your answer to the point and avoid unnecessary articulation and cop slang.