If you have already started using HSTS to force users to your HTTPS website, the use of ‘preload’ is another simple addition as it only requires the addition of the keyword to the header.
Once done, you can either wait for your site to be identified (which can take a long time, or forever for less popular websites) or ideally, submit your hostname to be added to the lists preloaded in many modern browsers. The advantage here is that your users will never make a single request to your HTTP website and will automatically be directed to HTTPS.
An HTTP Header example:
Strict-Transport-Security: max-age=63072000; includeSubDomains; preload
Apache2 configuration example:
Header always set Strict-Transport-Security "max-age=31536000; includeSubDomains; preload"