Too many people will key up and talk, just to hear themselves speak. This is fine in a casual game or between games, but can ruin a team during a match. Remember, if there are 8 people on the same channel, every time you key up to talk, 7 other people are distracted. If you key up to talk, make sure it is more important than the distraction.
A good way to communicate is by short typed commands. If every person on the team knows the codes, it is often quicker way than talking to convey a message. Long drawn out typed messages are a waste, because by the time you are done typing, the information is udually irrelevant. By using a mix of short typed messages, and short, concise voice communication, the relevance and spped of communication is greatly improved.