There’s a lot of information to keep in your head if you’re writing a book. There’s even more if you’re writing a trilogy or a series.
I happily wrote seven books without having a single style sheet… and then I got published.
The first book to be published (not by any means the first book I wrote) was duly delivered, went through the editing stage (content editing, that is) and then, when the story was as good as we (the editor and I) could make it, it went off to be copy edited.
At that point I started to get questions. Was it jumpgate, jump gate or jump-gate? Should telepath be capitalised or not? Was it Arquavisa or Arquevisa because I’d spelled it both ways. At that point I realised that although I thought I’d (mostly) been consistent (except where I hadn’t), it wasn’t immediately obvious to the copy editor.
Also there were words of phrases that I’d appropriated that meant something slightly different in my universe. House gold was a type of beer. Telepath was capitalised when it was an implant-enhanced Telepath, a psi-tech, but not when it referred to a natural telepath or telepathy. The Folds (capitalised) was the proper name of that supposedly empty space between jump gates (not hyphenated), but foldspace (not capitalised) was a type of space, not a proper name. Jump drive was not hyphenated to jump-drive unless it was a compound modifier.
All that and more.
I didn’t have a style sheet. It was a rookie mistake, and one I’ve not made since.
The copy editor of Empire of Dust had to make a style sheet of every name, unusual phrase etc. and the publisher very kindly passed it on. I used it as the basis of a series style sheet for all the Psi-Tech novels. I’m still using it.
Every character name is on there (twice – listed as Fred SMITH (m.) and SMITH, Fred (m.) so I can find it whether I look it up under surname or forename. (Surname always capitalised, just so I know.) Every hyphenation is on there where there’s a choice of whether to hyphenate or not. Every place name is on there. Every unusual phrase is on there, for instance:
‘Juno LAKE (f. Sofia Lake’s dtr married to a nice couple)’, or
‘Orphena – dryer than Orphena’s twelve moons (saying)’, or
‘dirtsider’ for someone who is planet-bound.
So every time you start a new book have a file open for your style sheet. Every time you decide whether or not to hyphenate a term, stick it on there. Every time you introduce a new character, or invent a new place, stick it on there. Every time you use a new swear word, stick it on there (especially if you decide to use frell or frack instead of the obvious four letter word).
Since mine has become a series style sheet, if I kill off a character I note it on the style sheet (and which book they die in), so I don’t accidentally have a walk-on character appear while dead, which would be very embarrassing.
I use Scrivener to write my first draft (and probably second), but my style sheet is a word doc. I use a twenty-three inch screen, so I can have Scrivener and Word open alongside each other while I work. And, of course, Scrivener incorporates places for your research and your character files, so you don’t need detail on your style sheet, just enough of a reminder so that the copy editor knows what’s what.
Whenever I deliver a finished book to my publisher I send the latest version of the style sheet. It saves a lot of questions. I don’t always get the same copy editor as I had for the last book, and even if I do, they aren’t guaranteed to remember what went before any more than I am.