Don't play with the same people, that's really the only way of being unpredictable, even then if you've ever participated in high level sports, or anything for that matter as the skill level increases, you expect your opponents to be better, and therefore they will generally follow similar strategies, since its proven to work.
Going back to poker specifically, at higher leveled games, and therefore higher stakes at hand, its not unknown for the players to have studied the psychology of humans, and therefore attempt to look for these triggers which the player isn't even aware they are doing themselves. The fact is, our body gives off more indications off subconsciously, than we do while we are consciously thinking. The only way you can truly become unpredictable, is learning what your body does, identifying it, and then training it via muscle memory to prevent "leaking" these indications. There's a few books out there, and podcasts which talk about this side of the game, and generally we are talking about the higher staked games here, rather than your local pub get together game.
There are so many different games to train your communication skills. I have already written about one of these games, this is the Russian-Ukrainian psychological game "Mafia". The game "Mafia" allows you to train the skills of bluffing and lying.
This popular game has even been featured in a sci-fi feature film (Mafia (Survival Game):
https://youtu.be/IRrN5MQoxpQ.
It is also helpful to get training in acting. If you are a professional player, you can pay for the services of an acting teacher.
The instructor will purposefully teach you the art of bluffing while playing poker.