If you want to design high quality UIs, read this book (Macintosh Human Interface Guidelines)[0] and ingest the concepts it explains. Even though it's not 100% applicable to a brand new software product, it may as well be -- most of the principles are totally applicable, and if you grasp the concepts from this book you will hopefully understand how to design a clearly-understandable user interface.

[0] https://dl.acm.org/doi/book/10.5555/573097 (click "PDF")