I really like "the design of everyday things" by Donald Norman. It's more focused on design in general, than what you're asking for, but I think the fundamentals of design is a prerequisite to become a good UX/UI designers
It teaches several ways to prototype design, how to evaluate whether your design is efficient, and how to develop a design oriented mindset
It not only helped me make better designs, but also made me a better coder, because I started thinking about my code as a product to be used by others
I was going to make the same suggestion. This book is one of those that seem like the insights presented are mostly trivial and obvious, but then you notice that it has completely reshaped your perception of a class of problems.
Plus, it's popular enough that there is a good chance you can find it at a library. (In fact, the first time I read it, I got an older edition from a library. I since bought a newer edition to re-read.)
I'll fourth or fifth this book. This book is way more important than the color scheme or how many pixels something should be.
This is more of a high level approach
It teaches several ways to prototype design, how to evaluate whether your design is efficient, and how to develop a design oriented mindset
It not only helped me make better designs, but also made me a better coder, because I started thinking about my code as a product to be used by others