By default, Cloudflare is conservative with caching and only caches specific static file types omitting HTML and other resources that may also be static for some users. You can get maximum performance from Cloudflare and cache other non-static file extensions by using Page Rules.
Go to Cloudflare.com > Choose your domain (upper left hand side) > Page Rules > Create Page Rule.
Now you can set the URL to match for instance: "www.example.com/*". The asterisk (*) is a wildcard character that can match any characters including no characters. For example, once implemented this rule would apply caching to https://www.example.com/index.html.
Next after adding the "Cache Level" setting choose "Cache Everything"
Once setup all resources matching the "Cache Everything" Rule will be cached by Cloudflare. You can find out more about setting up Page Rules in our Page Rules Tutorial.
You can verify your "Cache Everything" rule is working by following this guide on How to tell if Cloudflare is caching an asset.
Cloudflare includes additional advanced configurations for the Business and Enterprise customer plans to facilitate more granular control on caching: Bypass Cache On Cookie and Custom Cache Keys.