I think SAers are good at having that anxious/worried look so why not use it to our advantage. Just carry that face through all your hands, good and bad - that's the key to a poker face isn't it? Even when you have a good hand think about all the ways in which your hand can get destroyed. Bring out your inner worrier and keep it by your side so you have a ever-worried face! :lol
What I do is try to slow down my movements. I find that when I'm feeling really anxious or nervous I tend to dart my eyes around the room nervously and my actions are really kind of jumpy and if I have to say something I talk really quickly coz all I wanna do is run. But if I make myself slow down and concentrate on doing that it actually calms me down and I think it's less obvious as well. Hope that makes sense? :|
Focus your awareness on each of the muscles in your face. Tense tightly and relax each muscle group one by one. once you are more aware of the muscles in your face and what they are doing just practice having them not doing anything. when you have anxious face try and relax your muscles one by one. Once you are practiced at that blank look you can add small differences intentionally to **** with people for a better poker face. like sly grin or eyebrow arch
Edit: Also be stoned. I used to take part in a weekly hold'em tournament and when i showed up stoned it really threw people off. Several skilled players told me they had no idea what i was thinking because could never tell if look on my face was even remotely related to the game.