Valid HTML and CSS
HTML and various reincarnations of HTML (with fancy names people put on their CVs to sound clever) are the basic programming language of every web page.
CSS is the new way of formatting and laying out the information. Despite having been around for years and being a much better way to control style and layout than using those elements of HTML it's not as widely adopted as it should be.
Websites that use CSS load faster, are easier and cheaper to maintain and the style and layout can be changed really quickly.
Both of these technologies have worldwide standards.
Complying with the standards means your site will display correctly on as many browsers and platforms as possible, will be read by as many search engine spiders as possible and will be able to be maintained by as many web designers and developers as possible.
Check your home page now:
Are there errors? Give us a shout we'll fix them for you and if we maintain your site we will make sure you don't get any more!
HTML Validation tool provided by the World Wide Web consortium.