Design patterns are structures and relationships that we use repeatedly in object-oriented projects. Understanding them can help you to design better (and thereby improve the development of your software) and design systems that are more complex.
The application of design patterns can improve the quality of the systems that are developed, because they are, in practice, tested and approved solutions to common problems within the programming.
With the use of standards, you can reduce coupling, improve the readability of your code, and increase the degree of reuse of the code. Standards also help other developers to understand your code more quickly.
According to the book Design Patterns: Reusable Object-Oriented Software Solutions, by John Vlissides, Ralph Johnson, Richard Helm, and Erich Gamma (the Gang of Four (GoF)), design patterns...