In my experience it is more difficult for my writing students to choose interesting controlling ideas for essays on similarities than it is for them to choose interesting controlling ideas for essays about differences (contrast). One key to writing about similarities is finding two topics that at first glance appear to have very little in common. Recently a friend who admires Fred Astaire shared a You Tube video about some mirroring that Michael Jackson did of Fred Astaire. Although this topic is not particularly academic, the video illustrates some interesting similarities between a piece of work by Michael Jackson and some work by Fred Astaire.
I plan to use this later this semester in my writing course when we work on writing about similarities. I will either use it at the beginning of the unit as a “buy in” or at the point when the class is preparing to choose their topics.