If you use Gmail on a daily basis, it makes a lot of sense to familiarize yourself with at least some of its keyboard shortcuts. You can see a complete list of all keyboard shortcuts for Gmail here, but we consider the following ones to be the most useful:
Previous message in an open conversation: p
Next message in an open conversation: n
Send: ⌘/Ctrl + Enter
Bold: ⌘/Ctrl + b
Italics: ⌘/Ctrl + i
Underline: ⌘/Ctrl + u
Compose: c
Compose in a new tab: d
Search mail: /