URL structure decisions you can't easily undo later
Shopify makes most URL decisions for you: products live at /products/, collections at /collections/, and you can't change those prefixes. That's actually a gift - it removes a whole category of debate. But the parts you do control matter more than they look.
What Shopify fixes, and what you choose
Fixed: the path structure. yourstore.com/products/product-handle and yourstore.com/collections/collection-handle. No amount of configuration changes this on standard Shopify.
Yours to choose: the handle - the last part of the URL. "linen-shirt-navy" or "product-38291-nvy-01" is entirely up to you (or up to whoever imports your products).
Handles are forever, in practice
When you change a handle, Shopify offers to create a redirect. That covers the old URL - but not the ranking equity that takes time to transfer, not the links in old emails and blog posts, not the feed entries that now mismatch. A store that renames handles casually accumulates redirect chains and orphaned links.
The convention matters more than the specific choice. Pick a pattern - say, brand-product-name-color for products, descriptive nouns for collections - and hold it. A catalog where half the handles are descriptive and half are supplier SKU codes reads as sloppy to customers who glance at the URL, and gives search engines less to work with.
The collection/product URL trap
Shopify can serve products under collection paths: /collections/dresses/products/wrap-dress-red. It looks logical, and it's the default behavior when customers click through from a collection page. But it means the same product exists at multiple URLs. Shopify handles this with canonical tags pointing to the /products/ version - which mostly works - but your internal links should point to the canonical /products/ URL directly. Most well-built themes do this; many don't. It's a five-minute check with a real payoff.
One decision to make today
Write down your handle convention - one line for products, one for collections - and put it where whoever creates products will see it. The convention costs nothing. The absence of one costs a cleanup project in two years.