This is a 'if I had only known' post. And it has absolutely nothing to do with my health.
Years ago, as I began to write, my DH showed me how to do a time line, the kind he used in his engineering job. I adapted it to my novels, and have used a time line on almost all of my novels. Now here I am, trying to finish a series, and with the time lines already disposed of, I have to rely on the binders I kept of major characters for each novel. Still, I'm finding that's not enough. Because as the story develops things changed. Original characters are no longer major and minor characters which have little or no information about them take a prominent role. And silly me! I didn't keep a record of those changes.
So, here is a suggestion. Even if you don't think about a series, doubt you'll ever write one, could care less, it's a good idea to develop a spread sheet, or data base for each novel, detailing each character. You can indicate whether they become important as the story proceeds. When I first wrote Heartsong, I never gave a thought to a series. But, I found I had to tell the stories of the other brothers, hence the song series. Now, I have to go back and read through the books - I wrote - trying to remember the characters that became central to the story. If I only had a spread sheet, or a data base to refer to, it would be so much simpler.
Today is a dark and gloomy day, not a day to think about dying, so I'm immersing myself in finishing the novel, and doing a dozen little things (well maybe half a dozen) that need to be done. An example - Over the years, I've collected rolls of adhesive tape, gauze pads, bandages, and they were scattered around the house, in the bathrooms, of course, but in the closets as well. Now, they are all together, in one spot. Need a band aid, a piece of tape, or gauze? I can now put my hands on exactly what I need. Just a bit of the organizing that I should have been doing. Procrastinator? Yeh, I guess so! (grinning)