Practice, practice, practice. Duplicate. Practice. Duplicate. Create.
If you aren't feeling very creative, duplicate the work of others. Heck, even if you are feeling creative, duplicate anyway. Try to copy the iTunes interface. Figure out exactly what methods and techniques are used to design certain buttons. Then move on to other parts of the interface. You'll learn about subtle gradient use, shadows, insets, opacities, font, color palettes, and more. Before you know it, you'll have duplicated the entire iTunes interface and picked up a huge skillset along the way.
Then do the same with the most beautiful websites you can find. And the whole time, tell yourself it's not impossible to design that beautiful website because somebody already did it. If you get stuck, google the specific problem. Somebody was in your place before. The only way to really learn design (or anything, arguably) is by doing. When I browse the internet, I subconsciously examine every single piece of the design and figure out how they did what they did. For most websites it doesn't take more than a few seconds because they're remarkably simple once you know a little bit about design. For those tricky ones, I look a little closer and can figure it out within a minute or two, sometimes resorting to opening the source and looking at how the images are sliced up. If something's really busting my brain, I'll fire up Illustrator and give it my best shot.
Eventually you'll figure out what works for you and what doesn't. You'll gravitate towards certain techniques and ditch others. If you're smart, you'll even end up with a "graveyard file" containing all the little pieces that you might be able to use in future designs. With that graveyard file, designing gets exponentially easier - it's like having a box of magical tools at your fingertips.