This is difficult to do and from my experience, those people that with extraordinary ability to control their emotions can only do this and often times they treat gambling as their career. If in a normal situation or other type of gambling games we can't control our emotion then being unpredicatable in poker is really impossible. Each of us has a 1 or 2 particular strategy that we follow in gambling, if we stick to that then in the long run our opponent will get used to it. To be unpredictable is to use different types of strategy as well as learning to be emotionless in different situations.
To learn how to hide your emotions, you can enroll in an acting improvisation group. This is the so-called stand-up.
Classes are held both in pairs (two partners) and in groups (several partners). At the beginning of the session, participants perform exercises that develop attunement with partners. Indeed, in acting improvisation, the main thing is not to interfere with the partner (not to pull the blanket over yourself).
This is a very valuable skill for the player. In some gambling games, the player needs to play not alone, but with a partner. It is important not only to skillfully hide your emotions.
Perfect alignment with your partner is also very important.