First of all, make the text easy to read. It should not become an eye test, especially on laptop computers and mobile devices.
The viewing area of the browser is much smaller than a normal printed page, so documents may have to be reformatted to fit this new environment rather and just dropping an existing document into a web page. Don't run the text the full width of the screen, as this creates long lines of text that are difficult to read. Text also needs air around it. That's why most printed documents have margins.
Don't use long paragraphs of text. It's hard to read these in printed form and even harder to read on a computer screen. Try to keep paragraphs to four sentences or less.
Use color to convey information or to draw attention to where it is really needed. Never use the underline attribute for text because it makes it look like a link.
Graphics attract attention because they draw the eye to a particular area of the screen. Why spend five paragraphs describing your product when a single image will tell people exactly what you are taking about? In an age of special effects and short attention spans, graphics are great, even necessary.
There is a downside to using graphics on the Internet. It's called bandwidth. The bandwidth of the Internet is the pipeline in which all your information flows. It's the speed that data moves between your site and the person waiting patiently at the other end. Therefore, be prepared to sacrifice some quality for speed. Avoid using large graphics that don't add to the content of the page.
Avoid putting too many interface elements on the same page. Some sites present the visitor with a bewildering array of image maps, buttons, text links and images to click on. The effect can be overwhelming.
While animated images can attract the attention of the visitor, they make the page load slower because they use big files that slow down the loading and viewing of the rest of the page. The page might sit there for a considerable time, totally blank, while the first animated image loads.
Because they have much larger file sizes than regular images, animated images take up a lot more of the Internet's precious bandwidth --- yet another factor in slowing down the web.
They also can be distracting, making it harder for the visitor to concentrate on the other items on the page --- and they can become less interesting over time.