The Prequel or Parallel Series Or; On the Importance of keeping notes

When I started writing this, I was thinking mostly my own experience in writing the Prequel that is Witchslayer’s Scion, but I realized that this advice can be used for supplemental novellas or shorts, and isn’t limited just to prequels. So for starters, let’s start with some definitions:

Prequels: Events-wise most of the story predates a work that comes out first – like the Magician’s Apprentice in the Narnia series, which chronologically came out book 6 but is book 1 in the sequence, or the...