the loop is the easiest after the stall turn. Simply put..

Get nice and high and straight and level forward flight. Pull back on the elevator. once the helicopter is traveling straightup start reducing pitch.

Once you get to the point of being inverted you should be at neutral on the pitch or even a little negative.

Keep holding the elevator stick back and when the helicopter start to come around just start adding pitch until it is level again.

Nothing to it, but remember to reduce the pitch, if you dont it will be really ugly....