It's all about being creative and coming up with the right ideas and this is something we all have to deal with, whether we are a writer, photographer, painter, web designer, fashion designer, film maker, interior designer, architect, etc.
I do think that lots of people combine their own ideas with the ideas of others or long forgotten experiences.
It's important do figure out what you want to express and who you want to target when you design a site. Making a list of words (on paper or in your head) is always a great way to move your ideas closer to what you actually want to achieve. You want to make a site about gardening? Make that list! You'll notice that these words will help you to find the right colors, shapes, composition, images, etc.
Making the transition from ideas in our head straight to a final design has always been difficult for lots of people and making a list can be really useful.
Using your eyes; I've noticed that I've improved my photography, web design and photoshop skills purely by looking. I've browsed hundreds of galleries, I've watched several shows on TV about art, fashion, interior design, etc and I've read articles and books.
Part of it is interest, part of it is to train my eyes to look beyond what I see on the outside.
Many times I want to know why I like something.
Take for example the photography forum that I always visit. People post their photographs and when I like something I force myself to reply in great detail why I like it. It has forced me to really think about what makes things work and what doesn't, which is very helpful in developing my own skills.
And you know what? Most people have an easier time to say what's wrong with a photograph, web site, art piece, but it's always harder for them to express the reasons why they like something. I don't believe so much in the "I dunno, I just like it" answers. Maybe it's not always easy to describe what you see, but you can always try to describe what you 'feel'.
I'm sorry if I don't have an easy answer for you, but it's because I believe that creating that effective look is something that can't be describe in just a few words.
My advice for you is; look around more often, ask yourself why certain things have more visual impact, experiment and read.
My experience is this; no single book or site can give you all the right answers. That's why it can be very helpful to have a broad interest in any form of design or art and over time you will discover (like I did) how much they all have in common.