What are the best mobile app icon design practices?

Make sure you communicate your application's purpose, and as Apple likes to say, personality, through your app icon design. It should be simple, using common motifs and iconography so your user is able to quickly identify either the brand (for existing corporations) or it's intended functionality (e.g. messaging apps using chat bubble motifs).

Strive for Simplicity and Clarity: When designing your icon, aim for simplicity and easy recognition, especially when scaled down. Steer clear of clutter and excessive details that could obscure the icon's meaning and make it hard to decipher, particularly at smaller sizes.

Equally important is understanding how contrast and color are affected at smaller sizes. Remember, most of these icons are about the size of your thumb, so while we're editing on a desktop, it's important to test how they'll be actually be seen by users.

Enhancing Visual Impact with Color and Contrast: When selecting colors for your app's icon, prioritize those that not only resonate with your branding but also captivate the viewer's attention. Opt for hues that harmonize with your overall aesthetic, reinforcing brand recognition. Additionally, ensure that the contrast between different elements within the icon is pronounced enough to facilitate easy identification. This contrast will help the icon stand out, even in smaller sizes or amidst other visual elements, making it instantly recognizable to users.

Especially important not just for branding reasons, but so your app isn't accidentally blocked. For example, your app may actually get flagged as "spam" if your app icon is identical, or eerily similar to those of other apps already submitted for review to the App Store. Avoid treading previous ground. Be inspired by, but don't replicate previous icon designs.

Create a Design That Stands Out: Strive for a distinctive design that makes your app instantly recognizable among its competitors. Crafting an icon that sticks in users' minds will not only help them recall your app but also make it stand out amidst the sea of other apps on their devices.

Testing and Optimization: Test your icon across different devices and screen sizes to ensure it remains clear and recognizable. Make adjustments as needed to optimize its visibility and impact.

Designing an icon that follow's the platforms guidelines has it's own set of benefits, and additional work to do. For users, it means a similar experience when switching across different apps. Your app icon should align with the user's "expectation" of what an iOS or Android icon should look like. For designers, this means having a deep understanding of the different icon sizes, dimensions, and boundaries used when publishing on these different platforms. Within the Apple ecosystem alone, you could be working with 5 distinct app icons at one time, each with their own set of restrictions.

Guidelines for Platform Integration: When designing your icon, adhere to the platform's design guidelines (e.g., iOS Human Interface Guidelines, Android Material Design) to ensure that it aligns with the platform's specifications and seamlessly integrates with its visual language. By following these guidelines, your icon will not only meet the platform's requirements but also enhance the overall user experience by maintaining consistency with the platform's design principles.

If your brand has a "dynamic" logo, this is especially relevant as it can help you showcase your app's personality and connect in new ways with your users. MTV, Google Doodles, and the MIT Media Lab have all done this before. Your app icon too can reflect the current season, a special occasion, or a major shift in aesthetic on a platform (e.g. macOS Big Sur shifting from flat to 3D icons)

Frequent Updates: Ensure your icon reflects the latest branding and design of your app. By doing so, you can uphold consistency and relevance in the dynamic app landscape, thus enhancing your app's appeal to users.