Use row groups to segment tables for style, accessibility, and printing.
Use colgroups and col to style entire columns .
Consolidate attributes ( tr versus many td s, and so on).
Enable incremental rendering with sized col elements.
Use the fixed table-layout algorithm where possible (NS7+, IE5+).
Simplify, unwind, and layer your tables for maximum speed. Provide useful content in the first table.
Use the table trick to raise relevance.
Use CSS to style cell backgrounds (version 4+ browsers).
Use GET where possible.
Shunt form defaults into CGI scripts.
Substitute optgroup select menus for DHTML hierarchical menus.
Use trailing slashes on directories.
Abbreviate your URLs.
Use compression where possible.
Here are some good sources for more information on optimizing HTML: