Jay Pipes, MySQL employee and co-author Pro MySQL, gave a great presentation to Google employees which covers a number of techniques for tuning performance on MySQL. His examples include debugging and analyzing problems as well as best practices for table and index design, query and join operations, and server variable adjustments.
It’s a little over 40 minutes long, but incredibly informative, whether you’re a casual querier or a power MySQL user. Though some of this stuff is MySQL (or MyISAM or InnoDB) specific, the majority of the content is essential material for the average database application developer.
If you don’t have time to sit through it (shame on you) or you’re looking to jump right to a specific topic, there’s a nice time-coded dissection of the talk over at Peteris Krumins’ blog. There’s something so appropriate about adding a search index to a video about MySQL optimization.