Rather than thinking about “PSD into HTML CSS …” Try thinking “I’ve got an image, my designer’s just handed it off to me, and I need to create a structure.” Don’t think code, think meta!
Take a look at that magazine you got in the mail the other day. Open to a random article, preferably one with pictures. See its layout? Someone designed that. It’s a one- or two-column layout, there’s a title, there are sections, there are asides or images… it’s all structure. Can you identify the components to that structure?
Put the article aside, flip to a full-page ad. Do the same with that. It has a catch-line (which is a form of title), it has information, it has images and graphs and fine print (which, in structure, might be a footer). Can you see the structural parts? Don’t worry about how they all lay out, first make sure you are able to identify structural components.
Every so often, I spin off into a rambling reminisce. It’s a thing. So back in the day, I was a much younger man, and my first non-farm, non-Radio Shack job? I worked in a graphic design sweatshop. Everything was printed on a compugraphic (which means print a line of type, then pick up scissors and paste it onto a paper layout), layouts were sized with a vertical camera, and pages were built by rubber-cementing the layouts onto massive proofs.
From there, I applied for a job making twice the money, but they had actual computers. I had to fake my way through the test (worked, as I’d had experience with Illustrator '88), but the big question they had after was, “everything’s there, but the sizes are all wonky. Did you use the z-scale we left you?”
End of story time…
So after the structural bits, which I had cold in the above story, you can start working on the cosmetic bits - font sizes, colors, images, positioning. They are two separate tasks. Folks often try to do both at the same time, and some folks can, but I suspect you may find it easier to break it down into the separate tasks that they are.
Find the structure, build the structure, then do the interior decorating. At least, that’s my 0.02