Call Captain Kirk.
Calling H.G. Wells.
One of the frequent issues I have while writing is continuity. Sometimes, it's a simple slip of the brain. Sometimes it's a major malfunction.
While writing THE ARCHITECT, I realized my time line wasn't clear, so I went back through and marked each day to make sure it was right. When I handed it in to my editor, she called me out, telling me I was missing days. But I wasn't! I'd checked! So I went back through and clarified which day was which because -- and this happens more often than not -- my timeline wasn't clear.
I'm about halfway through with the next EPITAPH installment, and as I'm going back through and checking for details that need to carry through the story, adding details that might be missing, I stumbled on a time warp. No surprises. So I started labeling the days at the chapter heads to keep them straight. I went from Saturday, to Friday, to Sunday, to Monday, to Friday. All these days in two chapters, which only encompassed the passage of two days. Wait. WHAT? Argh.....
Some people use Scrivener (a writing program) to help with such situations, and this is the first time I'd actually wished I'd written the darn book in the program instead of my normal meanderings in Word. So now, instead of writing "new words" to reach the end of the first draft, I'm rewriting chapters to correct the mistakes I've made.
How to avoid this in the future? One of my friends puts a date and setting stamp at the head of each chapter, which is probably the easiest way. Another option is to follow your outline. Some authors have plot points and chapters mapped out ahead of time, which is also a good way to stay on track. Some use sticky notes or whiteboards to keep their timeline straight. While I do outline to a certain degree, I'm largely a pantser (write by the seat of my pants), which is where I run into trouble.
How am I going to fix this? Adding author notes to what I've written/will write - for my reference - showing what day it is for every scene change. Unfortunately for me, that means a lot of extra work that I could have avoided had I been paying attention to what I was writing! Darn those characters for carrying me off!