I am a piano player and I can play by ear. I've done a lot of theory and I understand chord progressions quite well. However, when it comes to teaching people how to choose chord progressions what is a good method to string together chords for a simple loop-based phrase? I've discovered a couple of rules: starting on III or V chord will cause the phrase to sound modal. For some of my students their choices just seem random...because they are.
Note: I am asking this NOT from the point of view where you have a given melody and you are trying to match chords to it.