I think it's hard to 'learn' how to make designs look great.

Personally, I think you origionally have to have some artistic ability (As opposed to PHP programming, where you can be taught that). I think 'experience' is the word i'd use to sum up your answer.

You can do hundreds of tutorials, but it doesn't really make you any better of a designer (more just how to know the tools). But to have created your own designs, had them criticised, had clients compliment them.. is the way.

I remember when i started designing years ago. I couldn't tell what looked good and what didn't.. (Noobies for example, use LARGE shapes, LARGE text, gradients.. etcetc.)

But yes. Look at different sites (Maybe sites in CSS galleries?), and understand what makes a good design, first.