如何组织控制器以获得最佳结构(MVC)

Whats the best way to organize controllers. Lets say I have a user controller and a register action, should I have a process_registration action as well where I validate and process the data, or just do all processing within the register action itself. Should I have a validation/processing action for every action that requires it (register, process_registration.. etc.)Whats the best way to organize controllers. Let