Start with Clean, Semantic Markup

Clean CSS starts with clean HTML!

Use the right element for the job (h1-6, p, ol, ul …)

Less-known Elements

  Semantic meaning Usability & Accessibility
<blockquote> Longer quote  
<q> Short quote  
<cite> Who is cited  
<samp> Output from computer  
<dl> Definition list W3C says use for dialogue and other not obvious purposes, others disagree.
<dt> Definition term
<dd> Definition data

Definition lists (<dl>) are like other list elements except you can tie together items that have a direct relationship with each other (name/value sets).

<dl>
   <dt>Event</dt>
   <dd>Date</dd>
   <dd>Description</dd>
   <dd>Venue</dd>
</dl>

Source: Keryx (X)HTML Elements Best Practice Sheet