HuFlungDung,
the rule of tumb I have been using is:
to go clockwise(G2) if you are cutting outside (like outside walls)and counterclockwise(G3) if you are cutting inside(like in a cavitie or hole,circular or rectangular, actually any shape). This applies for finishing cuts, for roughing you can go any way that save time; as long as you have coolant at all times.
Best regards,
GOMEZ107