To fully understand why mastering the art of the effective UI is so important, let's look at some of the things your app's UI can help you achieve, if you get it right.
If you follow best practices and Material Design guidelines, your app will reflect the UI principles the user has encountered many times before in other Android apps. Your users will feel instantly at home and also understand how to interact with many elements of your app, even if they're launching it for the very first time. For example, once the user has encountered a floating action button in one app, they'll know that tapping this button will give them access to important actions (also known as promoted actions).
Your app's UI determines how easily users can make your app do what they want. Create a UI that helps users get the value out of your app quickly and with the minimum amount of effort, and you're well on your way to racking up those 5 star Google Play reviews.
Although providing valuable content is still a crucial part of developing an effective app, remember that your app's UI is equally important. If your app's useful features and great content is hidden behind a clunky and generally unpleasant UI, then no one is going to hang around long enough to discover just how much your app actually has to offer.
Make sure you put as much effort into designing and developing your UI as you put into crafting your app's content and features.
A good UI establishes the rules of your app early on and sticks with them throughout. Once users feel comfortable interacting with a single screen in your app, they should be able to find their way around your entire app.
Your UI should ensure users never feel confused or frustrated by your app, by gently guiding them toward the tasks they need to complete next in order to get value from your application.
Whether your UI takes the subtle approach (such as using size and color to make certain UI elements stand out) or a more obvious approach (for example, highlighting the text field the user needs to complete next), you should make sure the user never has to sit back and ask, "So what am I supposed to do next?"
A good UI is like a helpful, non-judgmental friend, gently pointing out where you've gone wrong and giving you advice on how to fix it.
Imagine your app contains a form that users need to complete before tapping Submit. The user completes this form and taps the Submit button, but nothing happens. At this point, your app can either leave them scratching their head and wondering whether the Submit button is broken, or your UI can step in and show them what's wrong by underlining the one text field they forgot to fill in.
Because it isn't all about your app.
If you design your UI well and follow Material Design principles, your app will feel like a seamless extension of the Android platform and an extension of the other apps users have installed on their device.
By putting the effort into designing your UI, you can actually improve the user's overall Android experience. No pressure, then!