I agree with much of what has already been written, in particular with points such as consistency and not treating all patients as if they are clones that require the exact same approach. A sense of humour and a healthy dose of humility are also important.
Most of all, I think, I want a therapist who is interested and engaged in his job. Such a T will keep up with current developments in the field, and he is also more likely to treat me with interest and respect than a T who isn't really interested in the job he's doing.