This is advice for designers of websites that have a practical purpose, e.g., forums, shops, documentation. For purely artistic sites, or simply pointless (vanity) ones (not that I'm equating the two!), you might find the advice irrelevant.

If your site has a practical purpose (chiefly to distribute information and knowledge), then supporting that purpose must have overriding importance. The aesthetics of the site are much less important, and are intrinsically difficult to get right or be certain of due to the nature of the Web.

Here are some general principles of web design which I regard as essential:

• Remember that the web is not like desktop publishing. Consider, in particular, that the web designer's rendering (when he's testing his work) is not necessarily the same as the visitors'. (Note the plural!) There is no fixed page size or font size to work to, and your visitors will collectively want to see your work in many different ways. Indeed, some visitors will not see it at all, but hear it or feel it – but they will still read it!

• Which is more important? — the precise layout of your site as you see it in your development environment, or getting the information across regardless of the visitors' various environments? Whenever there is a conflict, go for the latter.

• Separate style from content. This allows the style to be chosen according to the characteristics of the rendering environment, and is particularly important when rendering non-visually – but it is also increasingly important for the many varied visual environments.

• Consider the occasional but ultimately certain unavailability of CSS, JavaScript, Java, Flash, media queries, SVG, and even images. Your page/site should remain usable even without these, i.e. do not use features in ways which make the page unusable by their absence.

  This stance is also useful in case you've accidentally fouled up your CSS for a visitor, so they can turn it off – usability should improve, in that case, even if aesthetics don't. Furthermore, search engines see your pages as (mainly) text.

You can see that the advice I give is mainly about not doing something that is unnecessary, particularly if it would render the page unusable for those who don't have the feature. This is because most of the problems I see in websites are solved by taking something out that accomplished very little.

You might think that following this advice limits your options (e.g., it leads to a less diverse Web), but I would say that many of those options (e.g., grand, multi-column, screen-filling layouts) were never really there in the first place, and are just fragile illusions (at least, without CSS3) – the Web was never diverse in that way, and those options were merely perverse, changing the Web into something which it shouldn't be. The fact that many people believe such options exist as normal capabilities of the Web is largely irrelevant, given that they go against its principles, and well thought-out international standards exist to support those principles. (I like to be bloody-minded on this point.)

Looking at it another way, if you follow my advice, be prepared to be disappointed with the results. This is a consequence of setting your expectations of Web design too high, probably due to being misled about the capabilities of the Web.