I've been doing web/desktop/server development for a while and have worked with many databases (mysql mostly). I've come to the point in my career when I need to have someone look at my queries because they're 'kind of slow'.

I believe it's now time to start learning query optimization. While I know the basics of index and joins etc., I'm not familiar with how to use, say, the EXPLAIN output to improve performance of my queries. I have not been able to find any online material that starts with the basics and takes me to application. Getting a book is not an option right now so I'm looking for tips about how to proceed with this.

I hope this question is general enough not to get closed.