The 3 C's of Communication are -
Clear
Always decide what is the purpose of the conversation and speak with clarity. If you know what you would like to convey and are clear with the ideas, then the communication is effective.
Concise
Keep it brief. Long sentences take the essence of the conversation away. Short, brief sentences which have clarity can still pass the message on.
Consistent
Don't be afraid to repeat if necessary, and communicate as frequently as possible.