Colors
Use of clean (i.e. white, light colors) instead of noisy (i.e. black, dark colors) background color
Reading yellow-colored text content over a black-colored background actually 'burns' the users' eyes, which should be avoided.
Use of appropriate font color that contrasts with background color
Yellow-colored text content over a white background 'burns' the users' eyes even more, and makes it much more difficult for reading.
Use of alternate colors for links, hovered (mouseover) links, and visited links
If the text color is black, employ a separate color for the links. This facilitates users in knowing where to click, and where to view the history of visited pages.
Font Use
Use of appropriate font typeface
Despite the controversy in preferring san-serif fonts (i.e. Arial, Verdana, and Lucida Grande) over serif fonts (i.e. Times New Roman, Georgia) for the web,there are no clear guidelines to specify a "must-use" for san-serif fonts. Use of font typeface for the website should be appropriate and fused with existing corporate imaging and design.
Use of appropriate font size
Users should not be squinting their eyes to read your web copy, and neither should they be using a magnifying glass to do so.
Sparingly use of bold/italic typeface
Bold/italic typeface is great for headers, or emphasis in short web copy. For a full running web copy with many bold/italic emphasized text, users will have difficulty in reading it, and tend to skip long sentences or paragraphs written in bold/italic typeface.
Sparingly use of capitalised text/title
Capitalised text are text is hard to read, and users tend to skip reading the entire web copy if the fonts are capitalised excessively.
Use of short paragraphs
A good rule of thumb is having 3 - 5 sentences in a paragraph, which is helpful in organizing content for presentation to users.
Use of appropriate spacing between paragraph lines
Paragraph line spacing affects readability significantly, in which a good rule of thumb is to set the line-height of your web copy between 135% - 145%.