Less is more

Being DRY means Don’t Repeat Yourself. Following this primary principle can keep you safe in the long term.

Stick with 3 colors

Try to use 3 main colors at max to maintain a perfect balance. Play with shades and tones if you need diversity.

Do

3 colors used, much easier to concentrate

Don't

4 colors used, hard to concentrate

Follow the 60% / 30% / 10% rule for the best color scheme balance. Use 60% as your primary color, 30% as secondary, supporting the main one, and 10% as the color of attention, used for CTA, etc.

Maintain a hierarchy

Avoid using too many fonts, their sizes, and inscriptions. Create a consistent visual hierarchy across the whole app.

Do

Hierarchy + font size matches heading importance.

Don't

1. No visual hierarchy.
2. Different fonts/inscriptions in use

Exception: This advice works for interfaces, commercial and technical projects well. Design magazines and blogs offer sets of headlines/paragraphs with 2-3 various fonts/inscriptions.

Do

Determine a specific font/size and use it throughout the application.

Don't

Content is inconvenient to read. Font and inscription have changed within the paragraph, it’s confusing.

Exception: You may use bold to highlight important phrases. Don't overdo it, all right?

Create consistent rhythm

Create a consistent interface rhythm. Document spacings and use them with the same consistency, from page to page.

Stay DRY

Multiplication of entities is a common mistake. It is terrible when multiple different components perform the same function. It brings more technical debt, UX and scalability issues.

Do

Create multi-functional components, change and expand them.

Know their rules

Google and Apple got totally different visual guidelines. As well as their user’s habbits and experience. It is imperative to consider its philosophy, principles, navigation, appearance, etc.

Apple Human Interface Guidelines

https://developer.apple.com/design/human-interface-guidelines/

Google Material Design

https://material.io/design/