Narrating a book is a peculiar activity as it requires you to balance tension and relaxation. You need to pay attention to detail while being calm enough to sound natural in the delivery of what’s going on and what your characters are saying.
It made me think of sports psychology books written by master archer Jackson Morisawa. In The Secret of the Target and One Arrow, One Life, Archery, Enlightenment he discusses how to take a relaxed Zen approach to focusing on the target. There’s a phenomenon called the ‘yips’ in sport which makes accomplished athletes tense up and miss a shot.
Something similar happens with narrating, where you know there’s a difficult word or hard to say phrase coming up—yet you pronounce it perfectly—only to stumble over easy words at the end of the sentence.
TOP TIP: When you make a mistake and curse out loud, bemoaning your idiocy, leave the rude words in for when you re-record it. Laughing at yourself is restorative!
Ssssssss….got a problem with sibilance? 
There’s an app to calm the hissing caused by an excess of the letter S. It’s called a ‘de-esser’ and has been around since 2014. The inventor Paul L also made a ‘de-clicker’ to remove the many irritating clicks that appear on a recording from movement and lip smacking by the narrator.
I downloaded both apps, storing them in the Effect Menu for easy access. I’ve been listening to my audiobook again, applying the de-esser to good effect. I wish that I’d found the de-clicker weeks ago, as I removed all my clicks by hand!
Updated De-Clicker and new De-esser for speech – Audacity Forum