I don't know if you have ever done acting or drama, but it helps on the ice. My husband and I both did high school theatre and recently got back into community theatre, I also did some modeling when I was young with still photos, and that helps too. My most recent theatre role involved a ton of facial expression, it was my primary communication with the audience and I could tell by their reaction if I was doing a good job or needed to step it up.
True facial expression means you put yourself out there and let the audience into your head. It is a risk, for some people much scarier than the physical aspect of skating in front of an audience. The same can be said to some extent of arm position, posture, ie-body language. There is a huge difference in arms that lift because your spirit is flying high with the joy of the music and your skate, and arms that lift because you and your coach put it in at some point. There is no program so boring to an audience as "smile here", "arms up here" I am yawning just thinking about it, and I see it constantly, even in very high level skaters.
For me, in acting as in skating, using previous experiences pulls out that emotion and hence, the expression. Often when I skate with my husband and we are comfortable with whatever we are practicing and are able to focus more on facial expression, I turn on my ipod and bring up past emotions in my mind with the music to practice my facial expressions. Those around me (including sometimes my husband) often give feedback that I looked joyful, lusty, filled with deep longing etc. I allow the combination of the music, the elements, and my memories draw out my expressions. I use my eyes a great deal. I use my mouth as well, it is not just a smile, it is "come hither" smile or an "pure joy" smile or "I am going to miss you" smile.
An excellent facial expression skater IMO is Katia Gordeeva, even when she was pretty young. Watch her eyes, they draw you in and her expressions are a brilliant combo of 1)Joy of skating and achieved elements 2) Interpretation of what the music means to her and some pre-planned expressions with the choreographer and 3) A seduction of the audience.
Seduce your audience. Draw them into your skating experience. When you listen to that music off the ice, let your face start to tell the story when you are alone and not skating. Then at the rink let go and take the risk. To do this you do need to have decent comfort with your program elements, but I often even find that emoting while listening to music really helps me relax enough to perfect elements as I learn them (ie-not over think them) Everyone has a different point I guess where they are comfortable enough physically to emote, but if someone has not reached that point and only has the physical down, then I don't really consider that program complete. Skating to me is silent acting, with the physical difficulty amped up by a thousand. Not easy, but it feels so good when you get to do it or see it done truly well.