Always approach the project from the point of view of the client’s needs. Here’s an example:
A client wants you to design a menu for his new restaurant. Your own preference is for really elegant and sophisticated designs, and you personally have no interest in doing other types of designs. However, the client’s restaurant is a low-priced hamburger joint, and the people who go there are not the type who would usually go to a elegant and sophisticated restaurant. So, your duty would be to design a menu that appeals to the type of people who goes to low-priced burger joints, despite your personal preference. So, either you work with the client, or you decline the project altogether. Trying to push your personal preference on the project would be a bad idea.
There ARE times however when a client just doesn’t know what’s appropriate and effective for his product, and if you feel that you have better suggestions, then present them to the client. However, don’t try to shove it down the client’s throat–if they don’t like it, they just don’t. And don’t ever insult the client by making it seem like you are better educated on the matter and that they are clueless. If the client has the foresight and the proper education, he should be able to see the merit in your ideas, but if not, then you need to reconsider if he’s the type of client you want to continue relationships with. If you really need the money, then just swallow your pride and do what he wants.