I have, rather late in the day, discovered how useful it is to have long strips of firm card on which to write details about the characters in my novel. It's better than scraps of paper or a notepad for this purpose because it means you have an excuse to buy beautiful, ready-cut and over-priced strips of card in lots of gorgeous colours. Also, because of their brightness and beauty, I don't lose them. Furthermore, the people in the novel who form a natural group, such as the main family or their foreign relatives or their neighbours or their friends, can each have their own colour. So when I'm struggling to recall aspects of a minor character's life/personality/habits from an earlier chapter, I can just find their colour and check the facts or add to them. All at a glance. (Or I could if I'd discovered this at the beginning.)
I don't usually make any lists or plans whatsoever, but I do love my cards. Just as I love my very weird spreadsheet for its coloured boxes. It may have something to do with colour. I have very bad eyesight, so perhaps I need things that stand out well.
Writing the novel, I reached the stage where I couldn't remember tiny quirks and individual characteristics, so now everything is added to the cards, if I remember to stop and do it. I also have a card for the street where they live. To a small extent, it forms a character of its own.
The other wonderful thing is that it gives a legitimate reason to procrastinate. I'm sure it's better for me to duplicate information on a blue or purple or pink piece of card when I need a pause from writing, than to wander through Amazon yet again, clicking away and adding to the ridiculously tall tower of books waiting to be read. I might count them one day, when I'm procrastinating again.