What makes a good UI website?
The UI design principals are:
Place users in control of the interface. Make it comfortable to interact with a product. Reduce cognitive load. Make user interfaces consistent.
What does it mean to improve the UI of a website?
A good user interface should be clean and uncluttered, making it easy for users to understand and focus their attention on the important parts of the page. Spacing lets the users know that the elements closer to each other are related and vice versa.