Busy family life entails a lot of plan-juggling, turn-taking, and scheduling, and it's impossible to keep it all in your head. If creating a "shower schedule" calendar in your smartphone seems a bit much, try this low-tech solution, from Rachel (who came up with this tip for herself, but I think is useful for the whole family):
I only shampoo my hair every other day, but I can't always remember if I washed my hair yesterday or the day before. (Days seem WAY longer than 24 hours with two small kids and a full-time job.) So, instead of standing in the shower every morning, trying to remember whether this is the on-day or the off-day, I keep one of my kids' bathtub crayons in my shower. I write on the wall what day it is, each day when I wash my hair. Then, when I get in the next morning, all I have to remember if what the day of the week is. If it's been two days since the day on the wall, it's a washing day. The crayons wash off with soap, so I just update the day of the week if I washed my hair that day.
Bonus: I can leave love notes for my sweetie with the crayon!
Another idea: If, while you're showering, you have a brilliant idea or sudden memory of something you need to do, make note of it with a bath crayon. Sometimes ten minutes in the shower is the only time alone you get all day. My brain tends to rev up during those moments, and this is a way to do something about it.