A few stats about mobile ecommerce:

 

Below are some of the best practices I already talked about which are specifically for mobile:

 

Optimize your forms for mobile:

 

This Shopify article is a good starting point to think about your mobile or mobile-responsive site.

 

Some thoughts on mobile testing…

Older devices are typically smaller, and thus the experience for those users is different. It’s important to make sure that your store works properly on all devices, from the smallest to the biggest screens.

The easiest way to test out your store is by using the Chrome browser “Inspect” tool, or Safari’s “Responsive Design” tool. This allows you to choose which device you want to see the site on.

However, that Chrome Inspect tool isn’t entirely accurate, and you might still want to test on real devices, if you have any. If you have an established brand, it might be worth the investment to have one of each popular smartphone from the past few years to be able to easily test on each of them.

There are also mobile testing services as an alternative to buying those devices yourself.