The principles involved in designing mobile sites can boil down to one word: simple.
There is more to explore now, for sure! Mobile sites have to be simple in design as people are viewing and interacting with them on small devices, and columns, sidebars, and complex backgrounds that are not only appropriate for, but also a part of a positive experience on a laptop or desktop, make the experience uninviting and inaccessible on mobile devices.
The second dimension of "simple" when it comes to design for mobile devices is that sites cannot be loaded up with plugins (like Flash), server-side scripting (like PHP) or complicated navigation schemes. Some of these features are supported in some mobile devices (Flash is supported in new versions of the Android operating system), but most are not. Moreover, mobile devices are limited in processing power, battery time, and other constraints that take us back to the watchword: simple.
Laptops and desktops on the one hand, and...