Why is simple attractive? That's because it simply works. Simplicity has always been associated with convenience in interactions between a user and a mobile application or website. Great usability has always been a result of great design. Flatness has been around for quite a while, but the topic went surging once Apple introduced iOS 7, which retreats from its previous principles towards flat design.
Why is flat perceived as a great solution for many kinds of software? Minimalistic approach has always been appreciated as the easiest to learn and use. At the same time, creating something minimalistic isn't a simple task at all. It's the challenging art of perfecting the intended design combined with functional filling; sifting out the unnecessary details to concentrate on delivering the content to users. Content and functions become the pivotal part, instead of extra textures, gradients and shadows; depth of the design relies on other elements. The result usually defines what people call 'user-friendly'.
Let's outline several useful notions for those who want to launch their own mobile application or website, sticking to the 'flat design' aesthetics. The emotional depth is made with color palette, hues, contrast and typography - all this can be enough to make an application impressive and recognizable.
Don't oversimplify, be consistent
It's quite simple to get your design oversimplified. But you really shouldn't. This can make the design look poor, and poor isn't minimalistic. An 'oversimplified' design can leave the user guessing and randomly tapping the screen - and that doesn't mean being user-friendly. A button must visually resemble a button, and a link must resemble a link; both must stand out against the page background. Shapes matter; be creative, at the same time without losing consistency within the whole application/website. You may use one simple effect as a unique peculiarity of your design.
Color and typography, step forward!
In flat design, any wrong hue or shape will be visible like nowhere else. With reduced volumes, effects, shades and textures, color steps forward as an element that identifies the software. Color palette is one of the most important issues in flat design. Choose carefully what colors you want to show; not only must the palette be good-looking and engaging, it must be visually identified with your company, your business, products or services, whatever the software represents. Colors and hues are tools for both carrying your message and waking users' emotions; it's a hard, challenging task for a designer, but once it works, it's worth it.
Typography has it the same, it occupies the remaining space on a screen; remember there's no room for anything unfledged in your software design. A thoroughly shaped Sans Serif typeface can make the software look one-of-a-kind.
Flat or skeuomorphic?
Undoubtedly, flat design is currently on the rise, some time ago adopted by live tiles of Windows Phone, now embraced by iOS 7 - and it looks really great if properly used. Type of application can influence. For example, graphics-oriented colorful games (or any other apps/websites for children) obviously aren't a good choice for being flat. Meanwhile, productivity apps and utilities might embrace it just perfectly. Skeuomorphism (a word that has been heavily overused recently) hasn't lost its relevance, it's loved by many people, and will be. Same thing with flat design. Both must be focusing on users, their needs, and the flawless experience of interaction. By the way, it's a good practice to let users try out, for example, two designs to choose what's better for them.
The user interface of your software product can reach a balance between these two approaches. You could also notice throughout this article, that flat design and skeuomorphism are referred to as 'approaches' rather than 'trends' - since they really are. Whatever you choose, avoid overusing either one, and create what's the best for your users.