The Do's and Don't's of Agreeable Conversation : Page 189
In both matters the rule must be that one must not talk one's specialty or one's shop unless the company is of the same shop or has the same specialty. A little thought as to what will please others, not one's self or one's clique, will make this self-evident.
A further obligation for a good conversationalist is promoting a variety of themes. Not only must he not talk too long at any one time, but, especially if he had a dominant part in it, he should also manage it so that no one topic will last too long. He should unobtrusively facilitate a sort of rotation of topics. This is, of course, the specific obligation of the host. But a good conversationalist is always the complement of the host. People often say almost with a feeling of guilt, "We talked about everything under the sun." The tinge of guilt comes from the Puritan tradition that anything which was fun must somehow have something wrong in it. The truth is that good conversation should glide along gracefully from topic to topic and sometimes back to the earlier ones.