Premium or Paid themes can be pretty expensive so it can be really helpful to use one of the free Shopify themes available on your store. The best Shopify Themes you can install for free are:

1. Dawn: The default Shopify OS 2 theme you can install for free on your website is great for most first-timers to learn and grow their business.
2. Publisher: This recently released shopify theme is perfect for big product inventories with support for a mega menu and stock counter.
3. Sense: One of my personal favorites, Sense is a free theme with built in rounded corners and a sense of depth that will make any health or beauty brand blush.
4. Studio: A simple and minimalistic theme that if used correctly, can shout premium from all angles.

You can explore more free themes on the Shopify Store at https://themes.shopify.com/collections/free-themes