Several years ago, when my daughter was little and we were struggling to cope with her autism, we used PECS cards and picture schedules to help her manage transitions. It didn't take long for me to realize that picture schedules were a great way for "NT" (neuro-typical) preschoolers to manage transitions, as well. I've been using movable picture schedules in my classroom for since then.
In almost every early childhood classroom, you'll find a written daily schedule at "grown-up" eye level for grown-ups to read. Few preschoolers can read these and even if they are able, they are likely posted way above a preschooler's eye level.
There are lots of great ways to implement picture schedules in an early childhood classroom. One of the easiest is to use a pocket chart and list the activities with a picture, similar to this one from Learning Resources. I would substitute the clock face for actual pictures for young children who are not "reading a clock" yet.
One of my colleagues made this one for her class. There is a clothespin that the students manipulate to change the current activity.
Last year, when my state Pre-K consultant visited, she mentioned that I really needed to have one that read left to right to encourage proper patterns of reading. My current schedule goes across and back again for a few rows, since I just didn't have the space to put one in one long length.
I use photos of the kids during each part of the day, so it is easy for them to relate to.
There is a velcro arrow that the "Timekeeper" moves throughout the day.
Some years, I randomly ask a student to move the schedule or assign it for the day, but this year I included it as one of our weekly jobs. Manipulating the schedule can be an especially helpful task for some children with autism or special needs. It is also very soothing for a child who has separation anxiety. They can look and see exactly what comes next and when "Mommy or Daddy is coming back".
Each Monday morning, my students are invited to pick a classroom job for the week and be in charge of that duty. Our "Timekeeper" gets to move the arrow at each transition time and gets to sport the "Timekeeper" job icon on their cubby.
Our "Timekeeper" icon
The schedule can be as complex or simple as your needs dictate. The goal is to make a schedule that fits your activities and needs. Be sure to post it low for little eyes and hands.