This is far from "Trivial." I teach Kindergarten and strangely enough, my students spend most of the lesson time on the carpet. I only have 3 tables in my classroom. One is for my small group and the others are for centers/workstations. The carpet has rows of colors and I excuse each row systematically.
I say, "Blue row, stand up." and they say, "Stand up."
I say, "Line up." And they say, "Line, line, line, hips and lips."
The students put one finger over there mouth and one hand on their hips. They should stand in line quietly while I excuse the other rows. They have opportunities to earn happy's:) or saddy's:( .
When they have this mastered, I switch it up and may call on the girls to stand up/line up first, people with blue pants and so on. The key is to switch it up. Have fun make it interesting, but do not change the expectation.
NOW, the most important part, and to answer your question about walking in line. Yes, I am an expert at walking backwards. I make several quick stops on the way to my destination to offer feedback on how well, or how we need to improve walking in line. These are chances to celebrate and get OH YEAHS or 10 finger WOO's!
Then, when needed,I use the 2 greatest words...LINE CHECK! The students repeat LINE CHECK and Make sure they are standing directly behind the person in front of them(Hips and LIPS). I began using this verbal cue about one month ago. It has been so effective that I have "caught" other teachers on my hall using this technique.
I hope this helps! Good luck,
Christina