What are the best methods to increase your metabolism?

I have a low metabolism and it concerns me, because I have to watch what I eat wherever I am... weather its with my family or friends, and whenever they offer me something rich I have to painfully say no because I worry that it would go down to my hips or my arms. I'm regularly exercising and having a constant appropriate diet, is there any other ways that would help boost up my metabolism? I've heard that green tea helps so does it? Thanks... any comments would be greatly appreciated.