there is special meta for ios devices. many of the same also work on android.
till, these are mostly for decorating shortcuts, except for the scaling markup; it's important to nail for a proper user experience. needless scrolling makes mobile suck.
use special css for mobile and sniff mobile stuff in js using tools like modernizer or ad-hoc detection.
scale back on image use; its cost user's money and slows down the page considerably.
you can clobber any existing background-image urls using more specific selectors to declare background:none; ...
emphasize features of the site that are likely to be used by someone on a small screen or in an on-the-go situation. for example if you're an organization, don't blather about your history on the landing page, throw a menu in my face, preferably something that offers simple single word options like [news, events, search, sections, about]...
bottom line: you don't have as much room to look pretty or do fancy stuff.
people don't want that. they want to get in and out as quickly as possible cause it a PITA using a mobile browser. the less painful you make it, they more they will love you.
(2013/5) HTML5:90.2% MOB:14% IE7:0.5% IE8:8.6% IE9:9.8% IE10:10%