If a teacher asks her students to line up (or form a line), will it be equally natural to express this idea this way:
Please make a line.
Please stand in a line.
Is the use of "make/stand" natural or unnatural? And is it common?
Either is acceptable, as is "Form a line", or perhaps "Get in line" (though that is rather direct).
If the purpose of the line is to wait in turn for something you could also use "Queue" as "Make a queue", or "Queue up for (something)"