Change standard quantity on product page from 0 to 1 (Magento 2)

--The easiest way is that we can change the input value from template: (override this template - not recommend)
vendor/magento/module-catalog/view/frontend/templates/product/view/addtocart.phtml

--The second way is the Magento default config: STORES > Configuration > Catalog > Inventory > Product Stock Options > Minimum Qty Allowed in Shopping Cart > > Add Customer Group > change to 1

Khoa's second option is the preferred one. Anyways, this sometimes does not work for bundles. There you have to also carefully check the bundles option's and quantities.

The logic for the default quantity could be found in

\Magento\Bundle\Block\Catalog\Product\View\Type\Bundle\Option::getDefaultValues

In my case a required option did not have a default option, leading to a zero default quantity.

--The second way is the Magento default config: STORES > Configuration > Catalog > Inventory > Product Stock Options > Minimum Qty Allowed in Shopping Cart > > Add Customer Group > change to 1

For some clarity on this question if the above doesn't work:

This was already done on the site I was working on, the issue was that on the individual product (in my case a configurable parent) under CATALOG > Products > PRODUCT > Advanced Inventory > Minimum Qty Allowed in Shopping Cart was set to NOT use this default config:

Changing this to Use Config Settings:

Changes the default qty to be 1 on the frontend: