Being a preppy has deep root on individual from an elite or high class universities or institution. Originally it a term that was used to northeastern private university-preparatory schools.
The article from the link below, says that preppy these days, refers to those who would want to look neat, clean and professional at all times without being too superficial.
Learn how you obtain the preppie look, on the same article.
Link: How to Look Preppy (preppy look); Clothes