The way to prevent blocking is discipline. Listen. Wait. Transmit. If you are blocked (you hear that whistle or screech), release the button immediately and wait before trying again. If you have an important message and the frequency is busy, wait for a gap. The few seconds you save by transmitting during a collision are worthless compared to the time wasted repeating garbled messages.

There is also a matter of respect and custom. In aviation radio, the rule is: the person who was speaking first keeps transmitting. Do not interrupt. Wait your turn.