You can easily find out 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:
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.