Great skins don't appear on their own - they only happen when the author has taken special care to ensure that their skin is the very best that it can be in these key areas:

• Usability
• The best and most effective interfaces don't get in the way of what you're trying to do
• Most windows have min/max/close at the top right - only change this if you know what you're doing
• Use sans-serif, consistent and reasonably large fonts
• Use backgrounds on which text is readable
• Make it easy for the user to tell when a click will have an effect, and what that effect will be
• Use the corners of the screen to good effect
• Treat animation with caution
• Choose a colour scheme and stick to it
• Use symbols as well as colours
• Sometimes the best identifier is text
• Keep the number of items on menus less than ten
• Technical excellence
• Complete, up-to-date skins are the best - supply your users with frequent updates
• Great skins tend to be 5% inspiration and 95% perspiration - you have to work at the details
• Small fonts may be less readable at higher resolutions - test for compatibility
• Always try to use less memory, disk space or CPU cycles
• Pre-blend alpha-blended or transparent images onto backgrounds
• Going from 24-bit to 256 colours can cut on-disk size by two-thirds
• Give your skin to a friend and ask them to review it for you
• Test your skin on different versions of Windows
• Solicit feedback, be around to answer questions
• Quality of Artwork
• If you want to know how a particular effect was done, ask the author
• Consider teaming up with someone who can do the parts you can't
• Ports are great, but obtain permission first
• Avoid putting any irrelevant images or text in your skins
• Use vectors, layers and other abstractions offered by your graphics program
• Originality
• Over-exposure to a style puts people off - be original!
• Don't be afraid to experiment
• Originality doesn't have to be graphical - use innovative skinning features and plugins
• User Customizability
• Help users make their computers look the way they want them to by providing customizations
• Consider offering different versions of your skin with different features
• Add comments/readme files where appropriate so others can modify your work to their own taste

It takes a lot of effort to make a great skin, but at the end of it you can look back on it and be satisfied that you created something worthwhile, to you and to others. And if that's not worth the effort of skinning, what is?

Some other resources you may find useful (mostly "for the Web", but many of the lessons apply to skinning):

• Jakob Nielsen's Column on Web Usability
• A Comparison of Popular Online Fonts: Which is Best and When?
• So, What Size and Type of Font Should I Use on My Website?
• Skin Optimisation Tips - an earlier article based on specific WindowBlinds optimisations
• WindowBlinds skinning guide - several articles on different aspects of WindowBlinds skinning
• DesktopX tutorial (outdated - another is being worked on)
• ObjectBar documentation

I hope this article has helped you. If you have any comments or suggestions for improvements, let me know!