When trying to increase customer reorders, you'll want to try things that improve customer behavior.
One behavior metric that works well is Customer Purchase Latency. This is the time between orders, usually a number of days.
If customers order every 100 days on average, you make a change, and they are now ordering every 90 days on average, you've just found a 10% behavior improvement. You'll get paid 10 days earlier, have a 10% boost in sales, and could potentially improve other metrics too.
Optimizing the latency can be difficult without a big-picture view of what you're saying (and not saying) to the customer. There's not going to be one spot you can tweak. You'll want to look at all marketing and communication you send to customers as well as what they're seeing in your storefronts.
The good thing about latency is that most Shopify stores haven't ever worked on it directly so there's often low-hanging, easy improvements that can be made.
The best starting points are your order confirmations and any initial emails you send. Every email and every communication can have an impact but the initial ones are the most critical (the first to second order transition is key). Improve those and your latency will start to improve.
Before you start, you'll want to measure where you're at. Calculating your Customer Purchase Latency by hand is possible but you'll have to subtract and divide a lot of numbers. If you have only 1,000 orders, you'll have hundreds of calculations to do. Even spreadsheets can struggle with the type of data latency uses.
It's faster and less error-prone to rely on Repeat Customer Insights. You'll also get some date and sales channel segmenting.
It comes with a 14-day free trial so you can see how it works and get some analysis right away.
Use cohorts to find out who the best customers are in your Shopify store
Repeat Customer Insights will automatically group your customers into cohorts based on when they first purchased. This will let you see how the date customers bought would impact their behavior.