It’s all too easy to forget the name of a sibling or pet or parent of a character who is mentioned once or twice in a manuscript. When you mentioned a character in Chapter 1 and not again until Chapter 12, what color eyes did he have? Can’t remember? When that happens and you want to refer to that person again, you have to reread until you find it. Or do you? Not if you create a spreadsheet before writing.
A spreadsheet will allow you to see all details of all characters at a glance. This helps in seeing whether all character names work together (you never want two names too similar, like Liam and Lenny). And the beauty of a spreadsheet is you can make a master template, save it and use it every time you write.
I create several spreadsheets because I use a lot of details. I have one for Main Characters, Protagonists, Antagonists, Mythical Creatures, Monsters/Beasts, The Holy Order, Map Info. You get the point. I assemble all of these in page protectors in a red 3-ring binder as well as files on my computer. Here are some pix of these spreadsheets and binder.
The other thing I created that I used A LOT when I first started writing, was a large map on a foam board. I leaned this on a table-top easel right beside me and referred to it constantly. On the flip side I had Character bios.
I hope some of this helps when you start thinking about a topic. It takes a little while to do this, but saves tons of time finding details later.
Besides having map files on the computer, I also draw out the streets of my fictional cities and put them in the binder. I scan them into the computer as well.
Other than the binder, this was the most useful tool I made in Prewriting. It was so useful I took a picture of it and put it on the computer. On the flip-side I had large bios with illustrations posted for each main character. As you can see in the picture, there are additional notes of place names and character names taped to the board.