Allow your customers to communicate with you through SMS. After they've placed an order on your shop, you can automate an SMS to be sent so that your clients can tell you the size they want, or time at which they want their goods to be delivered. 

When they receive it, they just have to answer and we will catch that answer an update their Shopify accordingly. With an almost 100% open rate for SMS, this is a simple and efficient way to collect customer information and to improve client retention.