Guidelines for designing more efficient Forms in huge systems

People who use the huge systems have a particular goal. Often the one thing that is standing between the user and his goal is a form. Because forms still remain one of the most important types of interaction for users on the web or desktop application. In fact, forms are often considered to be the final step of the journey to the completion of goals.
These are guidelines based on my research for designing more efficient forms to help users to complete forms quickly and without confusion.