Having some knowledge of psychology, you'll shine your shoes and "dress for success" before going to a job interview because you want to

You do these things before a job interview because you want to benefit from primacy effect. Primacy effect refers to the fact that the things that people notice first about other people are likely to be remembered more easily, meaning that first impressions matter. So if you turn up to your job interview in a neat manner, and you are very presentable, you will be more likely to get that job than if you looked like a hobo.