orientational metaphors rely on up/down or left/right. E.g., wizards where "next" is always on the right, and "back" on the left, and scrollbars where "more" is up.
ontological metaphors treat things in the computer as objects or substances, but not specific objects or substances. Files have sizes, errors "prevent" the system from doing something.
structural metaphors treat the computer concepts as real objects. E.g., filesystem as filing cabinet with folders that "contain" files.
conventional metaphors are those used without thinking (e.g., all those above). Novel metaphors are those that are perceived by the user.
metonymy is substituting a part for the whole, as in showing a person's face in a chat, or paintbrush icons for the mass colouring operation.
the authors add process and element metaphors as categories. You use an element metaphor (paintbrush) to clue the user into what process metaphor (colouring big chunks of pixels as though by painting) is active.
metaphoric entailments are the implications/limitations of the metaphor. E.g. the desktop filing metaphor includes "we have files and folders" but in real life, a file is typically a folder of pages but that is not part of the desktop metaphor.
Rule 1: know the entailments of your conventional metaphors so you can indicate any standard entailments that do not apply
Rule 2: with novel metaphors, you have to spell out all the entailments because users will not know what to do with your innovative "office workflow as camel's digestive system" metaphor
Rule 3: use as many entailments as possible (though all should be justified in terms of functionality), because the more they can successfully follow their knowledge of the metaphor, the more they'll trust it
Rule 4: orientational concepts structure multiple members of a group, so consider the implications: if you say good is up and put error messages on the bottom, you have to put success messages at the top. What's a success message?
Rule 5: use as few process metaphors as possible--a lot of process metaphors give a lot of entailments, and the user is overwhelmed. Minimize the number of process metaphors, and maximize their coverage.
Rule 6: base every element metaphor on a process metaphor so if your process is budgeting software then the user shouldn't see icons from the world of sport
Rule 7: understand the user's metaphoric world. Yes, Apple, on what bloody planet does the trash can turn into a CD burner? not this user's, that's for sure!