You do not have to prepare or do any homework—just making the appointment is already taking active step towards positive change. People who do nothing more than show up to their first session often feel a sense of relief that they are finally “doing something about it.” For your own sense of clarity, you may wish to write down the concerns that bring you to therapy and try to prioritize them, but again, even this is not necessary.
A key factor in successful therapy is the positive therapeutic relationship between client and counsellor. Almost all therapists will offer a free consultation so that you can get a feeling for whether you would like to work with them. And it really is free—you don’t owe them anything and it doesn’t obligate you to see them again. Almost all therapists will even encourage you to talk to a few different people before you decide; they really want you to be confident that you are getting the best possible care, even if that means you work with someone else.