You don’t have to add anything in UI. First clear your thoughts What exactly UI is and how it affects the User.
Learn basics of UI designing like color contrasts, Fonts, Sizes, Spaces, Backgrounds etc. You can refer the ready made UI’s on Dribble, Pinterest, Google etc.
Check these threads for more info . Top tools to make your UI Better - Guides / Resources - Kodular Community
Some useful websites for UI designing 
- Guides / Resources - Kodular Community