Google Music, like most of Google's services, supports keyboard shortcuts. Here's what you can do with them in Google Music:
Space bar : play/pause music
Right arrow : next track
Left arrow : previous track
Shift+right arrow : search forward in current track
Shift+left arrow : search back in current track
Up arrow : select item above current
Down arrow : select item below current
Delete : delete track
= : volume up
- : volume down
Alt+= : thumbs up
Alt+- : thumbs down
s : shuffle on/off
r : toggle repeat (off, all, and one)
p : make new playlist
i : make new instant mix from current track
e : edit current track
/ : search
? : display keyboard shortcuts
Now that you know how to get around Google Music with keyboard shortcuts, check out the shortcuts for Google's other services.