If you’re writing a series, refresh your memory of previous events by rereading the book’s predecessors. You’ll be surprised at the new ideas that come your way! I did this when I was writing the final volume to my Star Trails Tetralogy. It had been a while since I’d written the others, so I decided to read them to get myself into the flow to assure continuity, consistency in details, and so forth.
It was so worth it! I found an amazing number of little details to tie into the conclusion. At the time, they were just part of that particular episode, but when they fit future events, it was tremendous fun to find them.
Tying story arcs together in small ways feels good as an author and pleases your loyal readers as well. They’ll appreciate the reminders and when you tie everything together it leaves them more satisfied. It also brands you as a skilled, meticulous, and clever author. Life is full of interesting details, coincidences, and serendipity. Your stories should be as well.