The rule is simple in general: use the present tenses when discussing events in literary works. One situation where this gets more complicated is where you have to switch timelines because, for example, we enter events through a narrator's memories.
I set an exercise about this in an academic writing class, and almost all my students persisted in using the past tense, even after the narrator was no longer explicitly "present" in the event. Here's an invented example:
The story opens with a narrator remembering a snail that he saw on his front lawn. He asked his mother about the snail, which seemed strange to him because it didn't have a shell. His mother replied, saying that the snail was in fact a slug...
It would seem more natural to me to switch to the present tense already in the second sentence. But that means that the same timeline is evoked consecutively by two different tenses, which is a bit awkward. Are there any conventions for doing this gracefully?