Use shorthand properties, grouping, and abbreviation to optimize your CSS.
Use the hover pseudo-class and styled links or lists to create CSS2 rollovers.
Use table-layout:fixed for tables when possible and colgroup and col for speed.
Use CSS to color data cells in tables (works in version 4+ browsers).
Use CSS layout and positioning control and XHTML to separate presentation from structure to shrink your code, make your layout flexible, and raise search engine relevance.