This article identifies guiding principles in effective psychotherapies of patients with narcissistic personality disorder (NPD) and cautions against some common pitfalls. Individual psychotherapies of NPD patients were examined by both authors, who tested whether or not some principles, recommended in the literature, effectively promote these therapies and help these patients in moving forward with their lives and with effective therapy use. The authors identify a number of principles that were associated with more positive therapy development: helping patients identify goals and direction of their therapies, promoting a sense of agency, promoting a shift of focus to sense of vulnerability, and anticipating difficulty in developing and maintaining the treatment alliance. Common mistakes in these treatments are engaging in a power struggle with the patient, overindulging the grandiosity of the patient, directly challenging the grandiosity of the patient, and ignoring treatment-interfering behaviors. Identification of principles of effective therapies with NPD patients can help with the development of more effective treatment approaches for NPD.