Joshua Porter wrote, in 2012, a list of items that he considers the principles of the design of user interfaces. Despite being written in 2012, the points are still relevant, and I’ll publish here in two parts.
“To design is much more than simply to assemble, to order, or even to edit; it is to add value and meaning, to illuminate, to simplify, to clarify, to modify, to dignify, to dramatize, to persuade, and perhaps even to amuse.” – Paul Rand
Clarity is job #1
Clarity is the first and most important job of any interface. To be effective using an interface you’ve designed, people must be able to recognize what it is, care about why they would use it, understand what the interface is helping them interact with, predict what will happen when they use it, and then successfully interact with it. While there is room for mystery and delayed gratification in interfaces, there is no room for confusion. Clarity inspires confidence and leads to further use. One hundred clear screens is preferable to a single cluttered one.
Interfaces exist to enable interaction
Interfaces exist to enable interaction between humans and our world. They can help clarify, illuminate, enable, show relationships, bring us together, pull us apart, manage our expectations, and give us access to services. The act of designing interfaces is not Art. Interfaces are not monuments unto themselves. Interfaces do a job and their effectiveness can be measured. They are not just utilitarian, however. The best interfaces can inspire, evoke, mystify, and intensify our relationship with the world.
Conserve attention at all costs
We live in a world of interruption. It’s hard to read in peace anymore without something trying to distract us and direct our attention elsewhere. Attention is precious. Don’t litter the side of your applications with distractible material…remember why the screen exists in the first place. If someone is reading let them finish reading before showing that advertisement (if you must). Honor attention and not only will your readers be happier, your results will be better. When use is the primary goal, attention becomes the prerequisite. Conserve it at all costs.
Keep users in control
Humans are most comfortable when they feel in control of themselves and their environment. Thoughtless software takes away that comfort by forcing people into unplanned interactions, confusing pathways, and surprising outcomes. Keep users in control by regularly surfacing system status, by describing causation (if you do this that will happen) and by giving insight into what to expect at every turn. Don’t worry about stating the obvious…the obvious almost never is.
Direct manipulation is best
The best interface is none at all, when we are able to directly manipulate the physical objects in our world. Since this is not always possible, and objects are increasingly informational, we create interfaces to help us interact with them. It is easy to add more layers than necessary to an interface, creating overly-wrought buttons, chrome, graphics, options, preferences, windows, attachments, and other cruft so that we end up manipulating UI elements instead of what’s important. Instead, strive for that original goal of direct manipulation…design an interface with as little a footprint as possible, recognizing as much as possible natural human gestures. Ideally, the interface is so slight that the user has a feeling of direct manipulation with the object of their focus.
One primary action per screen
Every screen we design should support a single action of real value to the person using it. This makes it easier to learn, easier to use, and easier to add to or build on when necessary. Screens that support two or more primary actions become confusing quickly. Like a written article should have a single, strong thesis, every screen we design should support a single, strong action that is its raison d’etre.
Keep secondary actions secondary
Screens with a single primary action can have multiple secondary actions but they need to be kept secondary! The reason why your article exists isn’t so that people can share it on Twitter…it exists for people to read and understand it. Keep secondary actions secondary by making them lighter weight visually or shown after the primary action has been achieved.
Provide a natural next step
Very few interactions are meant to be the last, so thoughtfully design a next step for each interaction a person has with your interface. Anticipate what the next interaction should be and design to support it. Just as we like in human conversation, provide an opening for further interaction. Don’t leave a person hanging because they’ve done what you want them to do…give them a natural next step that helps them further achieve their goals.
Appearance follows behavior
Humans are most comfortable with things that behave the way we expect. Other people, animals, objects, software. When someone or something behaves consistently with our expectations we feel like we have a good relationship with it. To that end designed elements should look like how they behave. Form follows function. In practice this means that someone should be able to predict how an interface element will behave merely by looking at it. If it looks like a button it shouldact like a button. Don’t get cute with the basics of interaction…keep your creativity for higher order concerns.
Following on the previous principle, screen elements should not appear consistent with each other unless they behave consistently with each other. Elements that behave the same should look the same. But it is just as important for unlike elements to appear unlike (be inconsistent) as it is for like elements to appear consistent. In an effort to be consistent novice designers often obscure important differences by using the same visual treatment (often to re-use code) when different visual treatment is appropriate.