Nestor is correct in his information regarding questions about specific skins. There is a bit of generic information around, but in my opinion, (and this is only my personal opinion) the challenges we face with skinning is that is it's mix of design and technical that affect it's look and feel.
You have good guidelines to create modules - and if you adhere to them, the modules will work but are often basic if you aren't experienced in developing, however they will not work if you don't follow the rules.
With skinning, there is technical aspects behind it too, but the skins will work, just look bad in most cases. And this is not to do with DNN, its' to do with understanding html and CSS in my opinion. Opening up the default skin file is where I start EVERY PROJECT.. this is no secret but I use that file - either the dnn-blue or grey skin and work from there - And why do I do it.. becuase is has all the code in there already for me to start with and then I remove it..
From a beginner perspective, the skinning document is very instructional if you take the time to read it. That's how I started with NO HELP from a single person to create anything. There are plenty of free skins around that can be opened and followed.. making small changes and seeing the results.
What I see we're faced with more and more are people grabbing these elaborate sites or templates and thinking they can create these masterpieces within a few hours.. and I can honestly tell you some projects take me 30 - 40 - 50 hours.. they can take alot of work to get looking really sharp and I've been doing this solely for about 2.5 years now.. and I'm learning every day still. This is where you need to push your knowledge of dnn a bit further to get around the final touches.
I don't want to sound like I'm depressing anyone, but honestly - the diversity dnn offers, deserves some time spent in learning the product so you can understand the behaviour of the modules so you can then decided how to layout your pages and see the results once you put content in. There isn't much you can't do if you were to print out the Skinning documentation and start with that, you can spend a few dollars and download some videos from dnncreative, I've not seen them so can't comment on them, and I've got a few for free, which I'll increase once I get my new server (performance is holding me back a bit) but I see more and more people coming in who aren't willing to start with the basics and move forward.
So what they do is think that because DNN is supposed to be easy to deploy, (which we're finding it's not as easy as we thought) we move on to skinning, which they think is just changing a few images on a site (and in essence it is) but to get a really high end site like we see on some of these featured sites on DNN, they have taken weeks to do for some people.
Most of my work is high end, sites that aren't supposed to look like DNN, sites that need to be integrated into custom module development, modules that need to be skinned just to name a few, and every day is a learning challenge.
So if I can give anyone a few pieces of advice in starting off your skinning skills -
Read the skinning document, and print it out and read it, have it next to you while you're working or keep it open to copy and paste the code into your site if required.
Make sure you have some content in your site you're skinning (that stops surprises later)
Copy and paste the default skins folder - any colour you like - and called it Test.
Download / Buy / Try a few skins to see the behaviour of them
Open them in dreamweaver or light type of html editor.. anyone who really thinks they can develop a good skin in VS is going to be sorely disappointed. Its' a developer tool, so set yourself up with a design tool that will at the very least give you some preview of your work. I've never met a professional web designer who uses VS as a design tool. It's cumbersome compared to DW. Sure it might cost a few dollars but even a cheap html editor will give you better results thatn desigining in VS from a designers perspective. And after asking alot of poeple why they use VS the comment is that it's free or cheap or part of the company developer suite - NOT because they love the enviroment or feel empowered working in it.
If you're not sure about working with CSS, then use background images to get your experience up and work with the standard menu for a while. There is nothing wrong with using image background and images with the skinpath in it to create your skins if you are struggling with learning CSS.