Currently, shop listings are arranged from newest to oldest. The order of the listings cannot be customized.
However, if your shop has more than 16 listings (excluding private listings), you can select 4 to be placed at the top of your shop's front page. To do this, go to "Listings" →"Featured Listings" to select the 4 products. Featured listings will then stay at the top of your shop page, increasing their exposure.