Assuming the main reason you're coaching someone is to help them improve what they're doing, job #1 has to be making sure they don't get worse.  This is why it's so important to understand when you should focus on content, sequence, or emphasis.

The difference is in the amount of lead time.  If you try to get people to do things without enough time to do them right, you run the risk of hurting their confidence and making things worse than they would have been without any help.

• With enough lead time, you can coach people on content.  They can change what they are planning to say or do.
• With less lead time, you may still be able to coach sequence.  Even though they don't have time to re-think, re-write, or re-script things, they can alter the order in which they say or do things to improve their communication.
• With even less lead time, you can still coach emphasis.  Even with content and sequence set, changing the emphasis can alter the communication significantly.

Don't think for a moment that I'm talking about someone with the title of "coach".  This applies to anyone trying to help anyone else get better at almost anything they are trying to do.