Psychotherapy takes many forms, but all therapeutic approaches are intended to assist people in changing the ways they think, feel, behave and relate to others. In my opinion, the best therapies affect all those elements of a person. Research consistently shows that the single most important factor in determining the effectiveness of therapy lies in the ability of the therapist to promote a positive relationship with the client or patient. This relationship serves as a "container" in which to do the therapeutic work.
Many different types of professionals perform psychotherapy and counseling: social workers, psychologists, psychiatrists, nurses and pastoral counselors. The types and variety of post-graduate training a professional obtains is an important aspect of their qualifications-- sometimes more so than their formal degree.
Current psychotherapeutic techniques are classified along different dimensions. For example, one distinction considers the length of treatment, either in length of time or number of sessions. One simple categorization has to do with "brief" and "long-term" approaches. While this sounds clear-cut, there is no consensus about the length of time that constitutes a brief therapy approach. Some practitioners believe that 10 sessions is a useful marker, while others use the 20-session limit. Any amount of time over 6 months is usually considered of the "long-term" variety, but even that is not held as an absolute.
Another therapeutic distinction considers the expected goals of therapy. Is the goal to return the client to the pre-problem state or maximize their functioning beyond how they were functioning prior to the onset of distress? Other therapeutic dimensions relate to the manner that an individual's problems are affected by, and affect, other members of their family.
Psychotherapy is a very complex endeavor with scientific, artistic, and most importantly, relational elements. I think it is essential for any therapist to be comfortable and proficient with many different approaches, as the saying that "one style does not fit all" is absolutely true when it comes to psychotherapy. It is the therapist's responsibility to ensure an environment where therapy can be approached in an individualized and collaborative manner.
When looking for a therapist, feel free to ask them about their training, formal education, level of continuing education, and philosophy of treatment.