Playing a poker face is the basic way to act unreadable in the game poker even though you have a good card you won't show your emotions instead act as if you will lose. Just playing mind games with your opponents will make them bait your bluff. In the end if you don't want this kind hastle play online so you don't have to worry about your facial expressions.
Yes, but that's not easy and the bluffing doesn't end on that, it's much complicated than you think. Bluffing is all about reading and analyzing your opponents card, and then the bluff comes after that, I meant, you can't bluff totally if you only know your card but not your opponents cards, what's the point right?
Based on the gambling movies that I've watched, there was a girl gambler who's face is all serious because she knows what's his opponent card is, that's why her bluffing is effective. I've searched it on how to do it and all you have to do is to know arithmetically the number of cards and the patterns of it once it get shuffled and distribute. It's not easy, it's not always accurate, but I think it's worth to try than to bluff without any basis.