With me, I usually have a rough idea of what I want the site to look like before I begin. I usually do rough layout using MS word and then I use photo editing software to create a design concept, for example look at the attached image, its a rough concept of the new skin I am doing for my website.
I think move things around a bit, try different colours till achieve what I really like. Sometimes like you suggested, I spend hours sometime days on a stuff that I end up discarding
