User interfaces should be as simple as possible.
Interfaces should represent the user's task in as natural a way as possible, such that mapping between computer concepts and the user's mental model is reduced. This helps facilitate the user's navigation through an interface (this is the most important aspect of a good interface). This can be accomplished by matching the placement of objects and operations that should be accessed in a sequence with the way users will most effectively do things. Task sequences can be enforced by the user interface, but it is normally better to allow the user to control the dialogue sequence as much as possible.
Ideally, you want to present the exact information the user needs (and no more) at the exact time and place where it is needed. A proper task analysis can be performed to identify this information required by users to perform all of their tasks. This primary information warrants a spot on a single screen, whereas, the secondary information can be relegated to secondary screens. Additional pieces of information are something users will have to look at when they search the screen. This slows down their performance. Generally, if information is used 80% of the time it should be on the primary window, otherwise put it on the secondary window. This is the "80/20 rule".
A simple rule to follow when determining the amount of information that should be present on a screen is "less is more". Adding information and data fields to a user interface can distract the user from the primary information. Every extra piece of information in a dialogue competes with the most relevant pieces and diminishes their visibility.
The "less is more" rule not only applies to the amount of information displayed on screens but also to the choice of features for a program. A common design pitfall is to believe that "by providing lots of options and several ways of doing things, we can satisfy everybody". Every time a feature is added to a system, there is one more thing for users to learn, to remember, to understand and to search through when looking for the desired feature. Plus, the manual gets bigger, more intimidating, and harder to search. Alternatives for performing functions can be provided. But, care must be taken to ensure users can easily recognize the conditions under which each one is optimal so that they can consistently choose the optimal interaction technique without additional planning.
It is important to minimize the use of windows. Much time can be lost through the navigation of excessive windows, as well as the arranging of windows.
Good graphic design is an another important element in achieving a simple and natural dialogue for user interfaces. In order to increase the users' understanding of relationships between the dialogue elements and structure of the interface, screen layouts should use the gestalt rules for human perception. Examples include enclosing related groups of information with boxes and locating and grouping task specific buttons together. Principles of graphic design can also help users prioritize their attention to a screen by making the most important dialogue elements stand out (i.e. using bolder colours or typefaces, blinking objects, uppercase, etc.).
When using colour in screen designs, the three most important guidelines are:
An interface should also be usable given there are no colours. Redundant cues can be used.