There is an extensive literature on communication, much of it practical. In addition, I've also written some material for the archive. If in doubt, tell the truth. Tell it about yourself, and about the client. I've observed, often, a great irony.
Novices frequently undermine their credibility by trying to protect it.
This, at least, is my experience. Archived resources I've placed an overview of relevant communication skills in the arlist archive. Its title is communicn . It briefly describes ways of stating your own point of view, and ways of getting information from others. It also deals briefly with managing the process of an interaction.