I research the author and their previous books. If the world of the story is unfamiliar to me and based on real locations, I will do some online research to understand the geography and history of where the story is set. I also do a vocal warm-up before I start recording.
The story or plotline drives your style of performance. You need to reflect the pace of the story with your style of vocal delivery to engage the listener as much as possible. Fast and tense for high action sequences, slower and softer for reflective, emotional scenes etc. That said, a quiet, slow delivery can be extremely effective when describing a scene involving high drama so you need to be flexible and adapt your style of delivery to make the listening experience as engaging as possible.
Did you read The Making of Riley Paige book ahead of time?
Yes. Even though I've narrated all of the Riley Paige books so far and know the characters well, this was the prequel and included characters I'd not met before. However, when I am narrating a long-running series with recurring characters, I'll read the first two chapters in detail then skim read to pick out the storyline and any new characters and create a distinctive "voice" for them. However, even though you may know where a story is going, it's important not to give the game away by unconsciously anticipating what's about to happen with your tone of voice or delivery. You need to sound as surprised or shocked by the turn of events in a story as you want your listeners to be.
How do you approach reading multiple characters?
Performing dialogue as a part of audiobook narration is a very different animal to acting the part of a character in a full performance audio drama. Depending on the character in question, it's more about suggesting the sound of a character's voice rather than attempting to realistically sound like them. Clearly, I can't hope to realistically sound like a gruff, male police chief, but I can suggest his voice by making mine raspier and deepening my pitch. Similarly, I can raise my pitch for younger or even children's voices. With regard to accents, my default narrative voice is my natural British English RP accent however for dialogue purposes I can flex this accent from upper-class aristocrat to cockney London as needed. I can also perform a range of other accents.