Use filters

From 43FoldersWiki

Filters are a powerful way to keep your Gmail inbox empty.

You can filter based on the sender's email address, contents, subject line and even the to: address. The last is more helpful when you remember that RFC 822 says that a plus (+) can be used in an email address. For example, user+extrabit@example.org would be delivered to user@example.org, but the the extra bit left in.

More detailed info at gmailforums.

This is one of Brian Eno's Oblique Strategies.