This might seem obvious, but it's worth noting: It's also important that you like the therapist! Remember in school, how there were some teachers you couldn't stand, but maybe other kids like them, and some you liked even though your friends didn't? Therapists are the same way - no one therapist is right for everyone.
You should feel comfortable with the person and like you are making progress. If there is a conflict in the family, the therapist should not seem to be taking sides. You might have to try out a few before you find the right one. And if the whole family is going to therapy together, it won't be much good if one person hates the therapist!