Gray out Controls
It is not always pertinent to give a user access to all the functionality of a screen. Because of certain rules, it might not be applicable to have all controls available. An example of this could be the rule that a user cannot press the update button until after a field has been changed. In this case, the update button would be grayed out to demonstrate to the user that this button has a purpose, but it currently unavailable. This will lead users to understand the application faster.