As with paper documents, an effective way to write good pages for the web is to model them on existing good pages. You can easily examine the source text of pages that interest you, using standard facilities of browsers such as Netscape and Mosaic. Have a look at the Starlink pages. There are lots of them, and a good place to start is the central Starlink page at:
http://www.starlink.ac.uk/
From here you can go to most Starlink sites from the Sites link. There are also lots of Style Guides available to help you write good web pages. An example is:
http://www.w3.org/hypertext/WWW/Provider/Style/Overview.html