Up on C-Stick
Useful for attacking enemies in a small area. Must be used to trigger some switches.
Down on C-Stick
Useful for driving through a line of enemies and pushing blocks left or right.
Left on C-Stick
Useful for attacking on all sides. If you ever get surrounded I recommend using the cross formation. Can also be used to trigger switches.
Right on C-Stick
Useful for driving through a line of enemies while protecting a target. Also used for pushing blocks up or down.