Users overwhelmingly prefer sites which employ common
Web conventions (Nielsen, 1997). However, common standards are
very rare in web design. Some of the few that exist are:
Follow the standard hyperlink colors: blue for non-visited hyperlinks,
purple for visited hyperlinks, and red for active hyperlinks (but
if you have a site with a blue background -or any dark color- please
choose a color that can clearly be contrasted from the background
color. That is, if the choice is to either violate the standard or
not be visible, choose visibility!).
-
Place a navigational link to the homepage at the
upper left corner and bottom of each page.
-
Place the site's internal hyperlinks at the bottom
of each page (in addition to other places).
-
Images and text space should not cause horizontal
scrolling on lower resolution screens.
-
At the bottom of each page, place the date that
the page was updated and the URL address.
-
The text should facilitate the scanning of information.
-
Use ALT-Tags for graphics, especially for graphics
that serve as hyperlinks.
For an excellent and more detailed discussion of general
Web conventions, see the Yale Style Manual website: 
http://info.med.yale.edu/caim/manual/contents.html
Other fine guidelines include:
