When learning any new programming environment there will be lots of experimentation. Often being unfamiliar with the IDE becomes a frustration while trying to learn a new language like Objective C or learn new classes and libraries found in Cocoa.
Frustration with the IDE may cause you to give up. I know my impatience is the culprit!
So, here are three Quick Keys that were not obvious to me, and I was too impatient to drop down all of the menus or read the key stroke preferences to discover.
Switching between the source file and header file:
Option Command Up Arrow (Opt Command UpArrow)
Commenting code "in" or "out":
Command Forward Slash (Cmd /)
Move to the next argument in the auto-completion list:
Control Forward Slash (Control /)
⌘ Command key
⌃ Control Key
⌥ Option Key (aka Alt Key)
⇧ Shift Key