I'm enjoying The Non-Designer's Design Book - (http://www.amazon.com/The-Non-Designers-Design-Book-Edition/...), as a guy who spends hours trying to figure out why my layouts look like crap, this book has really helped me get to grips with the basics. Which is tbh, where you need to start. After that, just keep reading, designing and failing. Dealing with the inevitable frustration is key (see educational mithridatism). Learning how to use a good design tool also helps a lot. I'm playing with Sketch which is pretty awesome.

I guess in the end, there is no real linear path to learning design. You just sort of have to bumble along until you find your stride.

First, read The Design of Everyday Things. After that, I don't know.

I will say, though, that you won't ever come up with a good UI unless you watch people use it as early as possible. There is absolutely no substitute for sitting behind someone (preferably a lay person) and watching them try to accomplish whatever task they want with your UI.