How do you train your mind to positive thinking and happiness ?

How do intelligent people train their mind to work for themselves because I just feel like I have this really bad habit of overthinking and living life in my head. No wonder why I’m so slow and behind in everything. I’m not able to catch up with others and be mentally sharp and aware. I don’t know if the way we treat and talk makes a difference on our mindset. Like if you thinking positive do you become that sort of person. I don’t get it. I watch so many positive videos on motivation and read quotes but is like okay then what? And this cycle has become so toxic that I just keep going in this rabbit hole of finding clarity but what am I even doing with all this information