[krosaen]

I think it really depends on what you want to do.

1) Want to make user interfaces that are actually useful to people? Read up on product management, UX and interaction design. Important skills: articulating the problem you are solving and for what kind of user, and being able to validate whether your hypothesis is on point. Iterating before committing further resources to building a prototype. Conducting user testing sessions (rocket surgery made easy is a good resource for this).

2) Want to make a specific view / flow of a product inviting and visually appealing? Study visual design and typography.

3) Want to be able to build a functional prototype that looks reasonably good? Study frontend design / development. There are a lot of frameworks that could get you up and running.

IMHO going for (1) and (3) first is smart; if you can't prototype and evaluate a user experience that has a shot in hell of being useful to an actual user, being able to make stuff look pretty is kind of irrelevant (unless you are specializing and collaborating with engineers and UX people). In any of the above cases, at least knowing more precisely what you want to learn will help you do better googling, e.g "best books on visual design" or "best books on interaction design".