There are number of common design principles that, like design patterns, best practice over the years to build maintainable software. I'm up to describe some widely used design principles though out the post. Following common principle are extracted by the same book that I mentioned before ( Professional ASP.Net Design Patterns - Scott Millet ). Principles are as follows: Keep It Simple Stupid (KISS) One common issue in software programming is over-complicating a solution. So main concern of this principle is keep the code simple but not simplistic. Eventually this will avoid unnecessary complexities. Don't Repeat yourself (DRY) Main concern of this principle is to avoid the repetition. In other words this is all about abstracting out the common functionalities into a single place. Ex: If there is a price calculation method in a system. It should lay in a single place there. Tell Don't Ask The Tell, Don’t Ask principle is closely aligned with encapsulation and the assignin