Some guidelines - Teach, don't preach. All jargon must be explained . Pictures must be obvious and not require explanation. The use of language must fit the audience. Do not assume computer literacy for broad audiences.
Unavoidable failures cause repeated pain.
Failures that take time to repair cause much pain. Visitors from countries which pay for access by the minute are particularly intolerant of delays. If the home page is too slow to access, people will abandon the site entirely. Likewise, if navigation pages are too slow, people will give up searching for the main content. If the pages with the main content are slow to download because they contain huge quantities of irrelevant information , then the use may give up.