The Web/App spiral
Don't think of your Web site and your app as separate things. They're interlinked, both in the minds of your customers, and in the mind of Google.

When you think about your online presence, you shouldn't divide it into your Web site and your app. They're all part of the same thing, both in the minds of your customers, and in the mind of Google. When designed and managed properly, your site and your app should reinforce and complement each other.
Customers don't look at your site and your app as separate things. As far as they're concerned, they're all part of the same brand, just different ways to access it. (And, if you have a retail store as well, that's just another part of the same thing, not a separate commercial units.)
In this omnichannel world, customers don't care about technical issues or internal divisions of responsibility. They just want to use whatever tool is most convenient to find out what you're offering, make a purchase, track their deliveries, or communicate with you. In fact, they're likely to use more than one tool in the same transaction. They may browse on their phone while riding the bus to work. Then they'll make a purchase on their computer during their coffee break. And finally they'll keep an eye on their shipping notifications via the app.
The user experience has to be seamless and unified, allowing them to shift between devices and tools at will, and do what they want whenever and wherever it's convenient.
The Google view
Google's stated aim is to promote the content that their customers want. Their increasingly sophisticated algorithms are no longer simple checkboxes of headings, keywords, links and site traffic. What Google's ranking system looks for now are the elements that will make your entire brand attractive to people. The art of modern SEO and ASO isn't simply to outguess Google programmers: it's to understand what people are actually looking for.
What Google's ranking system looks for now are the elements that will make your entire brand attractive to people.
Most importantly, your search ranking and your app store ranking are interlinked. The higher your site ranks, the higher your app will rank. And conversely, the higher your app ranks, the more of a boost your site will get. Just having an app will give your site a noticeable boost.
Five tips for success
There is already a wealth of material about SEO and ASO, so I'm not going to go over all the techniques for boosting sites or apps. Instead, I want to concentrate on the specific techniques that focus on the interaction between apps and Web sites(including mobile Web).
- Have an app. Even now, many retailers still don't actually have an app. It may be because they think a mobile Web site is enough. (Pro tip: It's not.) Or it may be because they don't want to drive customers away from their stores. But the data shows that customers who use mobile apps actually spend more in-stores. There simply is no reason not to have an app these days. Customers expect it. And Google will reward you with a boost of 1-4 places in your Web site's search ranking.
- Design with omnichannel in mind. I've previously said that retailers need to think mobile-first. Most of your customers will be using a mobile device, whether they're on an app or going to your site. But more than that, the entire experience needs to be designed from the viewpoint that users will be switching devices, often mid-transaction. They may put items in a shopping cart on one device, and then complete the purchase on another. So make sure you're playing to the strengths of both platforms by providing mobile-specific features in the app and content that requires large screens on the desktop, but ensure that you allow free flow between devices as much as possible.
- Use the Web site to build app users. Google will reward you for sending your Web customers to the Play Store (and other app stores) to download your app. Make sure you have clear links on your site to download your app. In addition, think about how you're going to handle customers who are currently browsing on a computer: they can't simply download your app on their current device. Ombori's Bruce tool is specifically designed to deal with that situation, and early results show an increase of almost 20x in app downloads once Bruce is deployed on a site.
- Use push to engage app users. 80% of downloaded apps aren't used after the first week, so Google will be looking at your actual app usage. The more your customers use your app, the higher your site and app will both rank: unused or uninstalled apps won't give you any benefit. You need a solid onboarding strategy to get customers familiar with what the app can do, and to get them used to firing up the app instead of going to the site. Push is a powerful tool that will drive them direct to the app and kick-start that cycle.
- Drive traffic between site and app. Your site and app shouldn't live in discrete silos. Integrating them shows your customer that you're providing a seamless user experience, and that you're focusing on the brand and their needs, not the tool. If you need to send an app user to the Web site for a better experience, do so.
Designed and deployed properly, your app and site will build on each other. Your site attracts casual users and organic search. From there, your most loyal customers will become your app users. By using your app regularly, those VIPs will not only drive your app store rankings higher, but will also drive your web search rankings up, which in turn brings you more customers through organic search.
It's a powerful positive spiral that retailers need to learn to exploit.