One low-effort way to secure repeat orders is to add free trial samples to each order.
Adding in a low-cost, single-use product that's slightly different than what your customer ordered can whet their appetite for the other product.
For example, if I bought a tub of running nutrition (unflavored) then adding in a sample of another flavor or an electrolyte drink would make sense.
This can even be positioned as a kind of loyalty or VIP perk if you don't want to send them to everyone.
When it works you should see your Repeat Purchase Rate start to increase.
The easiest way to find and keep track of your Repeat Purchase Rate is through Repeat Customer Insights.
It'll also break that out so you can see how it worked for new customers vs returning customers.