The 4 Elements of a Winning Ecommerce Ad Strategy The Internet has opened vast retailing opportunities but advertising remains a mix of data and intuition.

There is no denying it, mobile is the new norm. Two in three American adults own a smartphone. Tablet users will surpass one billion worldwide this year. The average person spends more time on their phone and laptop than sleeping. With mobile adoption widespread, and people spending more of their time across multiple devices, it's no surprise that digital advertising spend in the US will total nearly $60 billion this year. Said differently, companies are heavily investing in engaging consumers across laptops, tablets and smartphones to win consumer attention and, ultimately, share of wallet on their path to purchase.

Digital advertising, also known as Internet or online advertising, can be a complicated space. With the numerous devices and channels available today for people to access content, consume information and make purchasing decisions, it can be challenging for a brand to succeed in engaging users and driving sales. But, it has never been as important as it is today. Ensuring the customer journey is seamless across all devices is a must for companies when people are fickle and have more options to browse and purchases than ever before.

Here are the four ecommerce strategies that empower brands to attract consumers and boost sales:

1. No stopping mobile.

At Criteo, we regularly analyze more than 1.4 billion online transactions to understand how consumers are behaving on all devices. Based on our data, we release a quarterly State of Mobile Commerce report, helping companies benchmark their success in ecommerce and make sure they're planning ahead accordingly. Just released, the Q3 report finds that mobile commerce accounts for 35 percent of all ecommerce transactions, globally.

The number is growing, and alongside it, mobile ad spend. It's projected that by 2019, mobile will account for 72 percent of US digital ad spend. Why? Because as consumers continue to turn to mobile for their online shopping needs, advertisers are looking to better engage them.

Companies must double down on a mobile first ecommerce strategy. This means having an easy-to-navigate and highly optimized mobile app in place. Mobile users spend 86 percent of their time in apps. Brands must engage consumers and drive conversion through this medium. Since consumers often toggle between devices along their purchasing journey it is equally important to deliver an intuitive and attractive mobile web experience.

2. Desktop remains a powerhouse.

While mobile is the newest frontier for digital advertising, desktop remains a powerful tool in reaching consumers and seeing them through to purchase. In 2014, desktop search accounted for 38 percent of overall digital ad spend (that's $19 billion), and desktop display accounted for 27 percent ($13.5 billion). Closely following was mobile at $12.5 billion.

Desktops (including laptops) now dominate the modern day corporate workplace, so when lunch hour rolls around, many tend to browse and shop for personal reasons while at their desks. While mobile shopping is no doubt on the rise, desktop remains a key device in the consumer's path to purchase. Also, desktop advertising plays a huge role in driving offline transactions. For example, the auto industry accounts for the second largest share of digital ad dollars in the US behind retail, yet most transactions are completed at a dealership.

Related: The 4 Digital Advertising Trends That Are Reshaping Advertising

3. All devices matter.

The buying journey involves many devices. Cross-device transactions in which consumers use multiple devices before making a purchase account for 40 percent of all ecommerce transactions. Someone may start browsing for a product on their smartphone via an app mid-day, then hop over to a tablet device later in the evening to do some more research through mobile web, but end up making a purchase on their laptop at work. For digital advertisers, consumers jumping from one device to another means each experience delivered needs to be relevant, consistent and non-intrusive.

Even though smartphones account for a majority of mobile transactions, tablets should not be forgotten. That's especially the case as companies release new innovations in the tablet market, such as Apple's new iPad Pro. Additionally, let's not forget about smartwatches. The market is in its infancy, but it's likely that soon consumers will be able to make purchases using their watches.

4. Attribution means ROI.

Many years ago John Wanamaker, a US department store merchant said, "Half of the money I spend on advertising is wasted; the trouble is I don't know which half."

That can't be said about digital advertising which, unlike traditional advertising, is extremely measurable. Nonetheless, in a world of views, clicks, buys, exchanges and more, it can be tricky to calculate what ads translate into sales, and across which devices.

An experienced in-house team on the brand side working with a reputable partner that is closely aligned on priorities and delivering performance-based results is the key to accurately attributing sales to digital advertising. Looking ahead, attribution is making big strides in understanding how online ads are impacting offline transactions, which is something advertisers also need to be well equipped to measure.

Related: Do Digital Ads Work? Who Knows.