I'm not there yet at all, pretty much in the same boat as you, so take this with a grain of salt. I have heard that in addition to all of the great technical tips about color/fonts, etc, the goal of an amazing design is to make it look difficult for the user to reproduce. If your design is something that someone would say "I could put that together in Microsoft Word," then it's just too simple. I think I read it in Simplebits or somewhere like that. Very soft gradients and rounded corners can each be incredibly subtle, but combined can give the effect that it's a professional design instead of something someone put together quickly. That's why you shouldn't ever use Times New Roman, because it's the default font for most browsers, and it shows the least amount of effort.