I think it really takes consistent practice to master "L-squared" mode (look and listen.) I have yet to master it because I still struggle with keeping it up during every encounter. What helps though is when I remind myself before or at the beginning of a convo to "look and listen". You'll find yourself doing one thing more than the other (looking more than listening or vice versa) but with time I think a happy balance can be struck!
Update: I am listening to episode #632 of the Art of Charm. It's really great, and will help answer your question above. If you haven't listened to AoC yet, I highly recommend it (especially Vanessa's episodes.)