I’ve previously blogged about the Rule of Thirds in general. I guess the rule applies to all photo-taking situation, including in macro photography.
However, you are more likely to get away with breaking the Rule of Thirds when shooting in macro than in any other photo shooting environment because you are faced with the depth-of-field constraint, giving you little room to manuoevre around the subject. I mean manoeuvre… gee, that’s a tough word to spell.
Having said that, you should not ignore the rule completely just because you can get away with breaking it.
Even when shooting in an extremely narrow depth-of-field situation, always keep in mind the possibility of throwing the subject “off balance” a bit towards either side of the frame.
Don’t ask me why you should do that. Just compare the first picture above to the one below decide for yourself which one is more pleasing to the eyes.
Of course you can always bend or even break the rule. But to be able to bend or break it effectively, you need to know the rule first. 
