MySQL Performance References

I have found this forum very interesting and informative, but a little beyond my current knowledge of MySQL. Before I get into specific scenarios and examples, can you recommend a few good resources on MySQL optimization that are more at the theoretical level? How did you all learn these things?

You can get some books ie “High Performance MySQL” or “MySQL” by Paul Dubois - books are good to get basic knowledge and have some theory.

And when you add your practice and a lot of resources you read - blogs, news etc.