Hmm... lools like my love affair with SQL related posts continues.
MySQL has posted an excellent resource posted called Top 10 SQL Performance Tips. Although, it is kind of a misleading name, since its a wiki, and everybody is able to post. Currently it's up to 84 tips, most of which look really great. Here is a small sampling:
- Don't use DISTINCT when you have or could use GROUP BY
- avoid wildcards at the start of LIKE queries
- Use a clever key and ORDER BY instead of MAX
- (And my personal favourite)... Don't use ORDER BY RAND() if you have > ~2K records :)
If you actually keep local copies of your database and then upload, you can also take advantage of suggestions such as "Use EXPLAIN to profile the query execution plan" among others. A great resource.