Pay attention to the cycles of the moon. More than any other astrological sign, Cancer's mood swings are in perfect harmony with the moon phases. Once you figure them out, you will be able to judge just when to tell him you dented the car and have him laugh it off.
Be conservative. This isn't about politics; it's about risks. The Cancer male is not a risk taker. He has a sharp analytical mind that works through problems quickly. This makes him great with money and investments. Because he is not a risk taker he is going to only go for the sure thing. This follows him into his personal life. He wants a partner who is a sure thing as far as fidelity and longevity. When he's in a relationship, it's generally permanent.
Be encouraging. The male Cancer needs constant encouragement both in and out of the bedroom. He tend to suffer from low self-esteem, though it is seldom deserved. He is more interested in making you happy than about pleasing himself, so if you have any suggestions make them gently, while reassuring him that you love him and he's great.
Pay attention to little things. The sign of Cancer is hypersensitive to both criticism and being taken for granted. If he is wearing a new suit, has just gotten his hair cut or has done something especially nice, comment on it.