Web Site Design

There is some great advice on accessibility at Dos and don'ts on designing for accessibility | Accessibility. In addition Inclusive - Microsoft Design is well worth looking at.

Cross Browser Testing

It is increasingly important to test websites on different platforms and with different browsers but once you start looking at specific devices then the permutations are huge. So use resources like Cross browser testing - Learn web development | MDN for help you and learn more. In addition Mozilla have been highlighting Free Firefox Testing on Real Devices recently (Feb 2017).

Icons

It is always nice if you website icon appears on your browser tab and when pinned in the operating system. So check out Favicon Generator for all platforms: iOS, Android, PC/Mac... for help building icons and HTML to support this.

Security

This is a huge area to consider when building websites, there is a lot to understand. I would suggest the most important thing and the starting point is to use HTTPS. You would do well to start with free certificates from Let's Encrypt - Free SSL/TLS Certificates and these can be automatically renewed to make life easy, hopefully your hosting account will sort this for you.

The next step is probably Content Security Policy (CSP) and for this I would suggest starting with Content Security Policy - An Introduction and then checking out Scott's CSP Cheat Sheet. You can also find a good introduction at Hardening Content Security Policy (CSP). One challenge of course is adding CSP to an existing site, for this Laboratory (Content Security Policy / CSP Toolkit) โ€“ Extension for Firefox is a great utility, however I do recommend watching the video, or at least the first part of it.

Handy Links

HTTP Observatory (Beta) - Mozilla Header checking
Analyse your HTTP response headers - HTTP Header Scanner
WebAIM: Alternative Text
Make the Web Work For Everyone โ˜… Mozilla Hacks โ€“ the Web developer blog