There are loads of useful shortcuts. Depends on the situation.
Ctrl + Home (PgUp/PgDown) are also really nice navigation shortcuts.
Left Shift + Right Ctrl to play from cursor position.
And my favourite combinations are [Shift + Alt + Z] [Shift + PgUp/PgDown] for fast selecting and [Alt + 1/2/3/4] to switch between clipboards.
And the more I get used to every kind of shortcuts the more I understand what’s the main feature in Renoise - workflow.