ICAO Doc 9432 - Manual of Radiotelephony
2.2 TRANSMITTING TECHNIQUE

2.2.1 The following transmitting techniques will assist in ensuring that transmitted speech is clear and satisfactorily received:

a) before transmitting, listen out on the frequency to be used to ensure that there will be no interference with a transmission from another station;
b) be familiar with good microphone operating techniques;
c) use a normal conversational tone, and speak clearly and distinctly;
d) maintain an even rate of speech not exceeding 100 words per minute. When it is known that elements of the message will be written down by the recipient, speak at a slightly slower rate;
e) maintain the speaking volume at a constant level;
f) a slight pause before and after numbers will assist in making them easier to understand;
g) avoid using hesitation sounds such as “er”;
h) be familiar with the microphone operating techniques, particularly in relation to the maintenance of a constant distance from the microphone if a modulator with a constant level is not used;
i) suspend speech temporarily if it becomes necessary to turn the head away from the microphone;
j) depress the transmit switch fully before speaking and do not release it until the message is completed. This will ensure that the entire message is transmitted;
k) the transmission of long messages should be interrupted momentarily from time to time to permit the transmitting operator to confirm that the frequency in use is clear and, if necessary, to permit the receiving operator to request repetition of parts not received.