Well here some of things I have come across which are just too good not to be used.
The fastest way to work with computers is using a Keybaord, Period.
you better learn the keyboard shortcuts, not just on gmail but otherwise too.
to enable them go to SETTINGS>GENERAL>Keyboard Shortcuts On
Turn on wild and whacky features in GMAIL
Go to SETTINGS>LABS> enable/disable features you like
I personally use - UNDO SEND, Offline, Old Snakey (you can actually play snakey from within game!!), Sender Time Zone,