How do I shield? I have this big problem that the Universe and someone (I mean some sort of spirit or something) is listening too much to my mind and now I want to do something so the Universe and someone don't listen to my mind. I get intrusive thoughts and I have problems in focusing, so I want to shield. How do I shield myself?
What you need is to see a psychologist. I feel like you're more or less describing attention deficit disorder or obsessive compulsive disorder.
Regardless, shielding can be done in many different ways. One in particular is working with your own chi. Simply put you want to meditate and focus your energy up and around whatever you're wanting to shield. To use your own chi for shielding you're going to need to look up some methods for programming, focusing, and controlling energy. You might also be interested in different methods to isolate objects, other people, or different areas of yourself and others so you protect something specific like your mind.