Principles in mobile user experience design
The main thing to keep in mind when designing a mobile app is to make it both useful and intuitive. If the app is not useful, no one has any reason to use it. If app is useful but requires a lot of time and effort, people won't bother learning how to use it. A good UI design addresses both problems. Mobile apps should be designed from the user's view. Users install your app because they need to solve a problem. Think about what it is our users will be trying to do and focus on their key goals. We want to remove all obstacles from their way.
User attention is precious, cluttering our interface overloads our user with too much information. Every button, image, and line of text make the screen more complicated. A simple rule of thumb is that there should be one primary action per screen. Every screen we design for the app should support a single action that the users value. This makes it easier to learn, easier to use, and easier to add to or build on when necessary. One hundred clear screens is preferable to a single cluttered one.
Helping users navigate should be a high priority for every app. Good navigation should feel like an invisible hand that guides the user along their journey. Even the coolest feature or the most compelling content is useless if people can't find it. Mobile navigation must be coherent. We should use the correct visual cues so that the navigation doesn't require any explanation and we want to make sure that each navigation element such as icon, lead to the proper destination. Mobile navigation should be consistent for the app, don't move the navigation controls to a new location or hide them on different pages, this will just frustrate the user. Mobile navigation should show the current location, not showing the current location is one of the most common mistakes. “Where am I?” is one of the basic questions users need to answer to successfully navigate.
Design finger friendly tap targets. Smaller touch targets are harder for users to target than larger ones. When we're designing mobile interfaces, it's best to make our targets big enough so that they're easy for users to tap. Create controls that are at least 7–10 mm so they can be accurately tapped with a finger. Such target allows the user's finger to fit snugly inside the target. The edges of the target are visible when the user taps it. This provides them with clear visual feedback that they're hitting the target accurately. Also make sure that there is enough space between tap targets.
Make the text legible. When compared with desktops, smartphones have relatively small screens, which means that one of the challenges of mobile design is to fit a lot of information on a small UI. We might have a temptation to squeeze everything down for a mobile design to provide as much information as possible, but we should resist the temptation. A rule of thumb for mobile is that text should be at least 11 points so it's legible at a typical viewing distance without zooming. Improve readability by increasing line height or letter spacing. A generous whitespace can make some of the messiest interfaces look inviting and simple.
Make user interface elements clearly visible. We should use color and contrast to help users see and interpret our content. Choose primary, secondary, and accent colors for your app that support usability. Make sure that there is enough color contrast between elements so that users with low vision can see and use our app. Make sure there is ample contrast between the font color and the background so text are legible. The W3C recommends that small text should have a contrast ratio of at lest 4.5:1 against the background. The W3C also recommends that large text, 14pt and up, should have a contrast ratio o at least 3:1 against the background. It's especially important in mobile app designs because users may be outdoors with low contrast on the screen because of lighting.
When laying out user controls, keep hand position in mind. Researchers found that 49% of people rely on a one thumb to get things done on their phones. Hand positions and grip should influence the placement of controls on a mobile design. It's important to place top-level menu, frequently-used controls and common actions where the user's thumb can easily reach. Conversely, place negative actions such as delete or erase, in the hard to reach areas since we don't want users to accidentally tap them.
Typing on a mobile is slow and proned to error. It's best to try to minimize the amount of typing required to use a mobile app. Keep forms as short and simple as possible by removing any unnecessary fields. Use auto-complete and personalized data where appropriate so that users only have to enter the bare minimum information.
Good mobile UX design should take into consideration that mobile devices have different screen real estate, lack physical keyboards, and are used in many different environments. When we take these into account, we realize that mobile applications have different needs than desktops and laptops and we can design our mobile applications accordingly.