Usability Standard 5:
Prevent User Errors

Even better than good error messages is a careful design which prevents a problem from occurring in the first place.12

Anticipate the user's needs with an information architecture that gives high visibility to the most important or popular features.

In the case of a highly structured sequential operation, such as buying an item or following step-by-step instructions, include context-sensitive help and clearly define the user's possible actions. With forms, employ tools that validate each field and point out errors on the fly as the user fills them out.