Airtime on aviation frequencies, whether you are communicating on a clearance, ground, tower, departure, en route, arrival or CTAF frequency, should be kept to a minimum. You need to make yourself understood in a quick, concise manner. You do this by using certain wording that all pilots should be accustomed with. But if you speak too quickly or not clearly enough, the controller may perceive a word as something completely different. Take the time to enunciate each number and word fully. You should also make sure to use ICAO’s recommended pronunciation of letters and numbers.