This is the question you need to be asking yourself.
Good interface design is a series of carefully thought-through decisions that were made with the user in mind. This is true throughout the entire design process: from the initial idea through defining requirements, sketching and wireframing, interaction design, and on into the visual design phase.
People tend to confuse art and design. Both require an instinct for aesthetics. However, visual interface design must communicate something to users so they can easily understand how to interact with the system in front of them. Because of this, good visual design goes much deeper than pleasing aesthetics— aesthetic decisions must support user needs and functional requirements.
Asking the question “why” can help you assess whether your aesthetic decisions are truly meeting user needs.
Why have I chosen a large font size for this heading?
Bad Answer: Because it looks good.
Better Answer: Because it adds variety to the page.
Best Answer: Because using a large font size for the heading creates a visual hierarchy within my interface, helping the user to easily scan the page and identify different sections so they can get where they need to go more quickly.
Why should I add a background color to this section?
Bad Answer: Because I saw it on Dribbble and thought it looked good.
Better Answer: To separate one thing from another.
Best Answer: I am using a background color to provide contrast and clearly delineate different areas on the page, with the intention of emphasizing the main work area and de-emphasizing secondary elements, so that the user can focus more easily on the important things on the screen.
Why should I make this element blue (or red, or green, or whatever other color)?
Bad Answer: Because I like blue.
Better Answer: Because blue is a color from our brand guidelines.
Best Answer: In color psychology, blue has connotations of stability, quality, and intellect. It also has calming properties. We want our app to be perceived as having all of these qualities, so we have chosen blue as one of our brand colors. By using blue for certain interface elements, I am reinforcing our brand standards and using color psychology to help our users trust us.
Why have I chosen to use linework icons?
Bad Answer: Because I found a cool-looking icon set and I wanted to try it out.
Better Answer: Because they match the aesthetic of our application.
Best Answer: These linework icons have rounded edges, lending them a playful quality in line with the feel that we want our app to have. Their open design also keeps the toolbar from becoming too heavy-looking, so that our interface retains the light, bright, modern attributes from our brand guidelines and doesn’t distract from the key interactions in this interface.
Honing Your Practice
For novice designers, it can be difficult to articulate “best answers” like the examples I have given above. However, asking “why” for each element on an interface will help you hone your designs and your designerly instincts. It will help you develop systems of meaning behind your designs, making further work on the project go more smoothly and quickly because you have a mental design framework to pull from.
It can also help you be prepared for the next time a client or stakeholder requests a change that you don’t support. Being able to articulate the reasons behind your decision, and being able to show that you have deeply thought them through, is often enough to persuade people not to make design decisions that you can’t get behind. So, to hone your design practice and become a better visual designer, practice identifying and articulating the specific reasons behind each design decision.