Rather than reaching for your mouse to click on the toolbar, use these access keys. Windows and Linux use Ctrl + letter. Macintosh uses Command + letter.

aSelect allxCut
uUnderline1Heading 1
2Heading 23Heading 3
4Heading 45Heading 5
6Heading 6kInsert/edit link

The following shortcuts use different access keys: Alt + Shift + letter.

nCheck SpellinglAlign Left
jJustify TextcAlign Center
dStrikethroughrAlign Right
u ListaInsert link
o1. ListsRemove link
qQuotemInsert Image
wDistraction-free writing modetInsert More Tag
pInsert Page Break taghHelp
xAdd/remove code tag  

Focus shortcuts:

Alt + F8Image toolbar (when an image is selected)
Alt + F9Editor menu (when enabled)
Alt + F10Editor toolbar
Alt + F11Elements path

To move focus to other buttons use Tab or the arrow keys. To return focus to the editor press Escape or use one of the buttons.