Most of it is capture. As I became more experienced I noticed that I retouched the skin (and everything else for that matter) less and less. Model, lighting, makeup and hair is the biggest part. The best models also often have the best skin. Styling is alot of it too. In the beginning you don't know why it doesn't look right, but often it's just the clothes are average or styled badly. Or how everything above is styled together as a whole. Everything is as important in this jigsaw puzzle.
The best and longest way to work on skin is actually with curves, blending modes, and masks. You brush away the high lights and shadows to a mid and even tone. It takes ages.
The best and quickest way if you are busy is just the clone tool. One seperate layers. Learn about blending modes.
Good retouching is knowing what to leave.
As for the 3D look, again it's mostly lighting. MFD helps but is not essential. There's a whole tonne of contributing factors. It takes years of experimenting and serious hard work to find this out so I don't think you'll find that many people really want to give those secrets out at the drop of a hat...Assisting is good for this reason.
My advice is to close your internet browser (now that you have a couple of basics in this thread) and open up Photoshop. Experiment. Learning fashion from books etc is futile. Make the effort to learn your own way, invest the time, energy and money into it and of corse with help from others along the way and you learn to do things differently. That's where individual style comes from. It's what makes you stand out from a very saturated market. Then YOU will see posts from people on websites asking how to do a particular thing that you are doing and only you know how to do. Really most of what makes something special is unique to someone because they have learned to do it themselves. It is their skill set - and that shows as aesthetic. Generic books give generic results. Generic fashion is quickly brushed aside in the the industry.
Goodluck and have fun. Learn to love the process and journey.