Identify text that should be styled consistantly in all your
documents. Headings are obvious candidates, but don't limit yourself to
just text in HTML tags. For example, you might want everything the boss
says highlighted in some consistant way. The important thing is to
identify all the things that require a special style. How these
things are displayed can be changed later using the style sheet.
Build the Style Sheets that describe how the "things" identified above
are actually displayed. Also include the overall page items like the
colour scheme and background image. You may opt for several different
style sheets, for example one for "title pages", another for "normal
pages", and another for "examples".
Build your web pages so they all use the appropriate style sheets. You
can add the older tags like <font> for compatibility with older web
browsers, but be sure to test that everything works properly when mixing
these tags with style sheets.