I have recently read a book about UI design, and I recommend it for developers who struggle to design approachable user interfaces.
If you are an experienced designer, the book is not for you. You probably won’t find anything new.
It does not have any water; it does not repeat itself and is structured well. It describes the basics and has many useful bits of advice that you can start applying right away.
It describes typography, colors, images, layouts, and other essential design concepts.
I recommend to read it and apply pieces of advice from it in practice. If you do not have any place to practice, create some simple pet project, and start practicing.
I bought it for $149, and it costs each cent. Additionally, I received three video tutorials, color palettes, icon, font, and component library.
You can also subscribe to their blog where they publish UI advice, tips & tricks periodically.
The only question I have right now is which tool I can use in practice to design UI. But this is another story.
Thanks to Adam Wathan & Steve Schoger.