You can easily find a huge number of the Internet resources with great recommendations on the UX and UI design. For example, the following 8 Golden Rules are supported by the platform user panels and the APS JS SDK used to integrate applications with user panels:
Strive for consistency
Enable frequent users to use shortcuts
Offer informative feedback
Design dialogue to yield closure
Offer simple error handling
Permit easy reversal of actions
Support internal locus of control
Reduce short-term memory load
A set of general design principles in the following documents is aimed to help you make the user interfaces user-friendly and consistent in accordance with the above rules. Also find their the illustrations of implementations of those principles in the platform user panels.