What are the most common UX pitfalls in mobile app design?
This is a very open ended question, and the usefulness of the answers will vary for every individual. Nevertheless, on a base level, I feel some of the most common pitfalls are:
1. Trying to adopt/scale-down web and desktop designs: In an effort to preserve "branding" and minimize expenses, I often find app designers trying to maintain the appearance of their app on the web or desktop. Not only does this present an unfamiliar UX for the user, but it serves to do more harm than good for the “brand”.
2. Applying cross-platform design language: There's nothing more annoying to the user than finding an Android app designed to be an exact duplicate of its iOS counterpart (I’m looking at you, Instagram). I imagine every platform user must feel the same way when they see a non-native appearing app. Avoid this at all costs. As Hilton Lipschitz has mentioned, pay attention to the specific interface guidelines of each platform and stay true to them as much as possible.
3. Slowing down the user with fluff: Mobile users generally multitask while using apps and would like the app to solve its purpose as quickly and efficiently as possible. Splashscreens and animations which take too long to complete (Like the Starbucks Android App) are one of the biggest pain points in using a mobile app and will have the user searching for a faster alternative.
4. Not providing feedback to user's actions: "Did I tap that button?", "Has the download started?". Prevent your user from wondering about the consequences of his/her actions. Provide appropriate audio/visual/haptic feedbacks for actions and the resulting mechanisms in the app.
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