The User Interface of any application (data-collection, e-commerce, brochure or otherwise) is comprised of four primary layers. Conceptual, Navigational, Linguistics and Aesthetics. Understanding each layer equally will enhance the level of success when presented to the User. The Conceptual is the base layer - the intent of the app. Above that, the navigational, how the User will traverses all screens. Next, Linguistics, here, the conversational tone and personality of the app will be most apparent. Lastly, Aesthetics, where all shapes, colors, interactions and layout are resolved. Collectively, these layers account for most applications in the wild today.
Base layer, the conceptual, is where (the what) all the of other layers are predicated on throughout the iteration process. This invisible layer is the intent. The driving idea. It is the potential solution to the targeted problem.
Once the app's general idea is fully baked, the first layer to be applied is the navigational. High rates of user fall-off or Abandonment are most often attributed to poor navigational schema and design. The taxonomy of the data, elements and screens must be well define and have sense flow. In doing so, the user's cognative load is kept low. Equating to a positive user experience.
The personality of the app will come through the words usage more so than any other characteristic. How the subject matter is communicated will be where the user either experience lowering or heightening the understanding of what the application is all about. If the target audience is primarily bankers, then the lingo would be wildly different in comparison to children's app. That is an extreme example, but the point is made clear.
Branding the experience is paramount and instantly assures the user that they are on the right site or using the right app. Certain colors will be secured for branded purposes, while other colors should be reserved for functional intent - such as green (success), yellow/orange (warning/alert) and red (failure).
