When I play poker, I imagine to myself, I just ate a very sour lemon.
My opponents are trying to guess what I am thinking, but they are confused by my twisted face.
They think I have bad cards in my hands. However, it is not! I have winning combinations of cards and my expression is just a bluff! This trick was taught to me by my personal acting teacher.
At the same time, when I have bad cards in my hands, then I act differently. I imagine myself eating a meringue cake. I have a blissful and slightly silly expression on my face.
My opponents think that I have great cards and lose.
An interesting strategy. As long as you don't go overboard, it can work.
Now you can not abuse this strategy, otherwise it can become a standard, and easily perceived by opponents.
Yeah, Using the same expression on the same card situation could make you even more predictable but putting different reactions or random reactions to a card could somehow make you more unpredictable.
There are people who are very good at reading their opponent's body language, They are very good at noticing some unconscious habits so, if I got opponents like this I am trying my best to have a poker face look or try to show random habits that I am not really doing.