I admit, I've been asking myself that same question for ages. Well, I suppose being a 'detective' means having a keen eye for detail. If you're a good observer, then that's basically half the mental journey already. Real life is very different from fiction, and unfortunately, Holmes and Conan/Shinichi do not exist in real life as living breathing humans, but they do exist in the form of books, manga, anime and movies. Through this, you can draw inspiration from them on how to be a detective!