Note, if you are on a Mac, substitute command for control.
Shift + Enter run selected cells
Ctrl + S save and checkpoint
Scroll up with the up arrow key. Scroll down with the down arrow key.
A insert a new cell above the active cell.
B insert a new cell below the active cell.
M make the active cell a Markdown cell.
Y make the active cell a code cell.
X cut the selected cell or cells.
C copy the selected cell or cells.
V paste the cell(s) which were copied or cut most recently.
DD (D twice) delete the active cell.
Z undo most recent command mode action.
Esc takes you into command mode
Tab code completion (or indent if at start of line)
Shift + Tab tooltip help
The usual commands for code editors;
Ctrl + ] indent
Ctrl + [ dedent
Ctrl + A select all
Ctrl + Z undo