One of the beauties of computers is the sheer volume of options that the user has---users can fit their hardware around their needs. One of the downsides to this is that different hardware, especially monitors, change the experience of a computer. One specific element is desktop wallpaper. What may work for one user may not work for another, due to resolution differences. If you wish to design a set of wallpapers for multiple displays, it is a good idea to understand how you should create your wallpapers.
Decide on your design. Knowing what you will be putting into your wallpaper ahead of time makes it much easier to create different versions for different displays. Sketch out your design before actually moving onto creating the actual wallpaper.
Start big. In your photo editor of choice, start with the high-resolution file first, as it is easier to downscale than upscale. As of 2010, 2560 x 1600 (width by height) is considered the high end of the resolution scale. This is a good starting point. Design your wallpaper at this resolution and save the file as the original.
Convert or resize for common resolution sizes. Common resolutions sizes include 1920 x 1200, 1600 x 900, 1280 x 800 and 1024 x 640. If you decide to resize, you can merely use the resizing tool in your editor of choice. This will not maintain proportions, meaning the image may look skewed. If you choose to convert, you will need to create a new file and paste your original work into the new resolution. At this point, you will need to either shift around graphics to make it fit the resolution or decide what can be cropped off.
Repeat the resizing process for all resolutions desired.
Keep in mind that the original 2560 x 1600 version will work with most any monitor, albeit a tad out of alignment. That said, the abundance of pixels will make up for any alignment issues.