Technology journalist (and various other things to make a living!) David Tebbutt has an interesting post on the 'rules' for interviews. They are a useful pointer, although they are only applicable for technology PRs (with my public sector or political PR hat on I would have a different list).
The only one that I would query is one of his "Examples of information which cannot be shared with a journalist". I don't understand why "Personnel information, PRACTICES or POLICIES" (my emphasis) is included in the list. As a PR I would counsel clients that these would seem like reasonable areas for a journalist to explore. As a customer I want the media to tell me about the employment practices of companies I might buy something from. It is relevant and interesting to know what policies they have on issues such as equality, redundancy, trade unions, outsourcing etc.
Hopefully David will respond and explain why this one is on the list.