The Companion's Companion (novel)

 was the fourth book in the Official Guide series, published on 6 April 2017 by Penguin Group, written by Craig Donaghy and illustrated by Dan Green. The book was stylised as an in-universe guide written by Clara Oswald for the next companion to travel with the Doctor.

Publisher's summary
If there's one thing the Doctor ought to remember, it's this: he should never travel alone.

And to help make sure he always has someone suitably brilliant by his side, Clara has compiled this comprehensive guide to travelling with the Doctor. Packed full of hints and tips on topics such as introducing the Doctor to your family, packing for life on the TARDIS and practising alien first aid, this guide will fully prepare you for life as a companion!

Worldbuilding
to be added

Continuity

 * Clara notes that the Doctor is scared during encounters with the Daleks (TV: Dalek, etc.)