cheat sheets.

ShortcutKey	Definition
c	Compose
/	Search
k	Move to newer conversation
j	Move to older conversation
n	Next message
p	Previous message
o or <Enter>	Open/Return to conversation list

y	Archive*
From 'Inbox,' 'y' means Archive
From 'Starred,' 'y' means Unstar
From any label, 'y' means Remove the label
* 'y' has no effect if you're in 'Spam,' 'Sent,' or 'All Mail.'

x	Select conversation
s	Star a message or conversation
!	Report spam
r	Reply
<Shift>+r  Reply new window.
a	Reply all
<Shift>+a Reply to all in a new window.
f	Forward 
<Shift>+f Forward new window.
<Esc>	Escape from input field
<Ctrl>+s Save
<Cmd>+s for Macs

Combo-keys
ShortcutKey	Definition

<tab> then <Enter>	Send message
y then o	Archive and next
g then a	Go to 'All Mail'
g then s	Go to 'Starred'
g then c	Go to 'Contacts'
g then d	Go to 'Drafts'
g then i	Go to 'Inbox'