If you mean you want to block others from reading your mind, all you do is say out loud and to yourself that you do not give permission to anyone to hear them. You can't be hypnotized unless you give it credibility. Same with psychics, why they ask you to give a bit of information about you, it's to gain consent from you.

If you really give a flying fuck then make sure it is who you are, that you will not give consent later, not that you can't but it should be a core principle of yours, like knowing 1 + 1 is two, you always never give consent until you do. If it's not a principle of you then you are still an open book. Just mean it, that's all. That's it.