Fifty percent of marketers admit that they aren’t leveraging mobile despite it being the fastest-growing marketing channel, while others still aren’t sure how to effectively target website traffic from iPhones, Androids, and other smartphones.

Those were two of the key takeaways from eMarketer’s Geoff Ramsey during a presentation yesterday on location-based marketing.

Ramsey presented a bevy of statistics, including research estimates that 75% of all mobile users will have a smartphone by 2016, and surveys that showed marketers said mobile is one of their top priorities. But saying and doing are two different things.

“Half of us are doing mobile, the other half are sitting on the sidelines,” Ramsey said.

There are two reasons for the gap between how many people use smartphones and the amount spent on mobile marketing, according to Ramsey. The first is due to the smaller screen size of mobile devices, which marketers have trouble figuring out how to utilize. Ramsey believes the second reason is that only 9% of marketers report feeling highly confident in their mobile marketing skills.

Ramsey covered four critical factors marketers should keep in mind to help make sure their mobile marketing initiatives are a success:

1. Mobile shifts power to the consumer.
Now, more than ever, consumers have the power to research everything from prices to product reviews. Users can instantly connect with social networks or call their friends to find out more about a product, or whether they’re getting the best price. That means brands must be transparent about their pricing and product reviews.

2. Mobile bridges the gap between the physical and digital worlds.
As Ramsey put it, smartphones allow users to interact with a brand in real-time. Maybe a smartphone user sees a billboard for a product, then uses an iPhone to find out more. Mobile devices shift the marketing paradigm because they allow users to interact with your brand immediately. The best mobile campaigns use these instant interactions as an opportunity to integrate with other channels.

3. Mobile must be integrated with other channels.
Before launching a mobile marketing effort, look for ways to sync that campaign up with social media, email, and even print advertising efforts. For instance, a mobile campaign might provide a coupon visitors can use online. If so, the mobile marketing campaign creative, whether through the wording or design, should be displayed on the website in order to leverage consistency and keep visitors on the “scent trail” of the promotion.

4. Mobile is the most personal channel.
Phones are more personal than other marketing channels, and a smartphone ad that appears at the wrong time with the wrong message can have a really negative impact. It’s absolutely critical to make sure mobile campaigns provide genuine value and service to users.

Make sure you ask users to opt-in to your mobile efforts, and then send them relevant information and offers they actually need. One way to do that: Ask those who opt-in what sort of offers they’d like to get, and what time of day they’d like to be sent an offer. Sounds simple, but it’s a great technique to make sure your mobile efforts don’t hit a sour note.