Should a Buddhist "have faith"?

In many religions it is common to say: "Have faith in God" or Jesus or Allah... In Buddhism we believe in Kamma, meaning that what happens to us is due to our past actions and it is usually not (or never) influenced by an external being. (It can change from school to school, some may pray and ask for things) So if there is something I want, something I judge important, should I have faith that it will come true? Or should I just do what I think is right and forget about it? What is the best way for a Buddhist to act in this situation? PS: Please ignore the fact that I want something, I know this could be questioned in Buddhism as the wrong way to happiness, but that would be a different question :)