Can you tap it?
Does it fit in the mobile screen?
Is your mobile site mobile?
Is your mobile site social?
Is your mobile site customized/personalized?
People don't use mouse clicks on mobile sites, instead they use fingers to tap it. Therefore any elements on the mobile site (buttons, links, pages, etc) need to be tappable. Imagine tapping the tabs on walmart.com and then take a look that their mobile site below.
Not only is the mobile screen much narrower than your monitor, it is also usually used vertically (if it is not for video/game purposes). Therefore a single-column vertical layout would be easy to navigate.
Unlike your desktop website that is usually accessed at a single location, a mobile site should be smarter to provide the most relevant mobile solutions. A "Local Ad" on the Wal-Mart mobile site that uses the visitor's location to serve up an ad for the nearest store can be much more relevant than a list of store locations and promotions.
This is a great way to increase interaction and chances for data collection on a mobile site, if you remember one of a mobile site's "weaknesses" is data collection compared to mobile apps. You can be really creative to make your mobile site social, through blog comments, social media tabs built in, a sign-in feature, etc.
A personalized tool is likely to be used more often. This doesn't mean you need to make this mobile site look different to each user, but to give them the freedom to customize it. The second to last tab on the Wal-Mart mobile site is "Shopping List", which is a great example of customization.
One last suggestion for a mobile site is "Testing it"! Always test your project before going public. If you don't own a mobile device with internet access, borrow a friend's for a few minutes or give FiG a call at (303) 260-7840. Not only are we able to test a site for you, but could build a completely new one or offer recommendations on how to improve your existing mobile site!