1. Aspect Oriented Programming – AOP
2. Don’t Repeat Yourself – DRY
Don't Repeat Yourself (DRY) is a principle of software development aimed at reducing repetition of information of all kinds, especially useful in multi-tier architectures. DRY code usually makes large software systems easier to maintain, as long as the data transformations are easy to create and maintain.
Violations of DRY are typically referred to as WET solutions, which stands for "Write Everything Twice".
3. Client and Server side validations could be done through Data Annotations in ASP.NET MVC3.