Get it in writing, keep it in writing.
When you have a face-to-face meeting with a client or project group, take notes. After the meeting, summarize your notes as brief bullet points and email them to everyone who attended or would have a vested interest in what was covered. This ensures that you all agree on what was covered.
When you have a phone meeting, do the same.
These simple points of documenting all communications in writing have proven to save enormous time and money, and to prevent massive misunderstandings and the resultant upsets and loss of business that inevitably come from not maintaining this policy to the letter.
Remember: The spoken word is in the air; the written word is always there!