The definitive guide to using phpMyAdmin is the book Mastering phpMyAdmin for Effective MySQL Management by Marc Delisle. You can get information on that book and other officially endorsed books at the phpMyAdmin site.
Third party tutorials and articles which you might find interesting:
Seriál o phpMyAdminovi
Having fun with phpMyAdmin’s MIME-transformations & PDF-features
Learning SQL Using phpMyAdmin (old tutorial)
Russian server about phpMyAdmin
Custom Themes
FAQ - Frequently Asked Questions