Not sure if this is exactly what you're looking for but I found this series to be incredibly helpful at understanding principles of design to make something attractive and functional.

Also, I can highly recommend using one of those "we spy on all your users and replay their visits for you so you can see how they actually interact with the site" tools. Luckyorange seems like it's gotten bad recently but maybe Mouseflow or similar. You'll learn more about how to improve the site based on observing 5 actual people interacting with it than from hundreds of hours theorizing and working on this perfect vision in your head.