In Bold: shortcut key
In Italics: basic use or definition
In Normal: Detailed action

1. c – [Compose] - Allows you to compose a new message. + c allows you to compose a message in a new window.
2. k - [Move to newer conversation] - Opens or moves your cursor to a more recent conversation.
3. j – [Move to older conversation] – Opens or moves your cursor to the next oldest conversation.
4. n – [Next message] – Moves your cursor to the next message.
5. p – [Previous message] – Moves your cursor to the previous message.
6. x – [Select conversation] – Automatically checks and selects a conversation so that you can archive, apply a label, or choose an action from the drop-down menu to apply to that conversation.
7. s – [Star] – a message or conversation Adds or removes a star to a message or conversation. Stars allow you to give a message or conversation a special status.
8. ! – [ Report spam] – Marks a message as spam and removes it from your conversation list.
9. r – [Reply] – Reply to the message sender. + r allows you to reply to a message in a new window. (Only applicable in ‘Conversation View.’)
10. a - [Reply all] – Reply to all message recipients. +a allows you to reply to all message recipients in a new window. (Only applicable in ‘Conversation View.’)
11. f - [Forward] – Forward a message. + f allows you to forward a message in a new window. (Only applicable in ‘Conversation View.’)
12. <Ctrl> + s – [Save draft] – Holding the key while pressing s when composing a message will save the current text as a draft. Make sure your cursor is in one of the text fields — either the composition pane, or any of the To, CC, BCC, or Subject fields — when using this shortcut.
13. # - [Delete] – Moves the conversation to Trash. via

To navigating faster in Gmail, here are some combo keys shortcuts: 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']. Hope this will quicken up things!