Keywords. On mobile devices, users type less, so your keyword strings can be more generic and shorter. Long-tail keywords are not going to be of any use because no one types in four and five-word keywords on a mobile device the way they would without hesitation on a computer. Beware of being too generic though.
Landing page. Mobile landing pages must be mobile-friendly. They don’t necessarily have to be mobile-only sites, but they can’t be loaded with flash (good luck getting that to work on an iPhone), involve heavy graphic-laden pages that take forever to load, or be filled with links that frustrate the user who is scrolling or enlarging on their phone.
Ad copy. Make it actionable. There should always be a call to action, but on a mobile device, people are so actively engaged in the search process that they couldn’t wait until they were on a desktop device. A sense of urgency is implied.
Location. Since many mobile searches are localized (someone is looking for a restaurant or a boutique or a gift shop near them at that time), emphasizing the location, proximity, or convenience is key. You can do this with a few different techniques, but regardless of the approach, the end result remains the same.
Bidding Strategy. Bidding, while the same in theory, is often a little different on mobile devices. Since every industry behaves differently, you might have to try both higher and lower bids than you have in desktop campaigns before finding the happy medium. In some cases mobile is more expensive, in some cases, it is less. I think, long term, mobile will be more expensive for more campaigns.
Click to call. Adding phone extensions that provide click-to-call functionality will boost conversion rates by making it easier for leads and customers to get in contact with you immediately.