Ugh! This habit of actors is the worst. It is so frustrating as an audience member (and a director) to be watching a character on stage, really trying to connect, and they stare at the stage. Why is that a choice at all?
I get it, your character is insecure, or shy, or distracted, or a little gassy… whatever. My point is, there are so many more interesting choices than taking one of your most important acting tools (your expressive little face), pointing it at the ground, and showing the audience the top of your head. You may have a lovely head of hair, but it doesn’t usually make us feel for you – unless we can see your roots, then we REALLY feel for you.
Characters feel all of the things mentioned above and more, but make sure you are using your tools to their fullest extent. Look almost anywhere other than down. The audience wants to connect with what your character is thinking and feeling. They have to see your face. Shy characters might not want to look directly at another character, but try looking up, look to the side, simply avert your eyes. Better yet, allow your character to struggle with where to look. Almost anything is better than looking down.