So you always wanted to become a GMail expert? Now GMail offers many tips on using GMail and making you an expert or as they call it Ninja. Google is offering four types of ninja belts : white belt, green belt, black belt and finally the master.
You can visit http://www.google.com/mail/help/tips.html and go through different levels of tips. You should start with white belt and slowly move on to the next level. The white level has 9 easy tips, green level has 12, black level has 11 and the master level has 9 tips.
If you want to keep an offline version of tips or want to print the tips out, you can download the PDF version of GMail ninja tips : http://www.google.com/mail/help/gmail_tips.pdf (592 KB).
These tips are absolutely free, so enjoy your ninja training.