When you're considering psychotherapy, you should remember that the most important aspect of the treatment, in terms of predicting whether it will be effective for you, is the relationship itself. A deeply trusting and cooperative relationship with your therapist must be developed in order for all the other things that need to happen to happen. So, first of all, find a therapist you like and feel understood by. That means calling up a few different therapists and speaking with them over the phone, maybe even going in for consultations, until you find someone who you feel like you can relate to.
The next thing to understand is that different therapists will approach the treatment from different angles. I've spoken with an awful lot of people who had “tried psychotherapy” and been disappointed by a therapist whose treatment style just didn't mesh with their own way of thinking. In some respects, the ability to adapt to the needs of the patient is the mark of a really good psychotherapist. But there is also an element of the basic theoretical underpinnings of different types of therapy simply not being a good fit for a certain individual's personal style. So you may want to look for a psychotherapist whose theoretical orientation is basically appealing to you.
There are three major theoretical schools in modern psychotherapy: Cognitive Behaviorism; Humanistic, also called Client-Centered; and Psychodynamic. Each of them approaches the patient and the treatment from a different place, and they will each feel very different to you in practice. There's been a good deal of research to try and determine which of these is the most effective, and it's pretty much all come back that they are equally effective, so I think you should simply go with whichever one seems most appealing to you (or whichever one your favorite and most respected therapist happens to practice.)
Cogntive Behavioral Therapy approaches the treatment from the understanding that we are all engaged in a dialogue with ourselves all the time. It happens automatically, and it's one of the main ways that we generate feelings and behaviors. That applies to positive feelings as well as negative ones, so a Cognitive-Behavioral therapist will attempt to help you identify the automatic negative thoughts that are making you feel and act in suboptimal ways. Once you're able to recognize the cognitive mistakes that have been lodged in your thought process, this type of therapist will help you to modify these ways of thinking, so that your automatic thoughts are more conducive to the types of emotions and activities that you want.
Humanistic or Client-Centered Psychotherapy approaches the treatment from the understanding that every person has an inherent tendency to grow and to improve—to self-actualize. And that all we need to activate our tendency to begin growing into better versions of ourselves is just a basic level of nurturance and empathy. So, a Client-Centered psychotherapist will gradually help you to experience the therapeutic relationship as a place where you will never be rejected, no matter what happens. They will allow you to explore your own emotions and come to your own realizations at your own speed, by providing you with the basic ingredient of simple, unconditional positive regard.
Psychodynamic Psychotherapy approaches the treatment from the understanding that we are all thrown into this world cold and naked, surrounded by omnipotent giants whom we are absolutely dependent upon for survival. From there, we simply do whatever we have to do to adapt to that situation—and we generally do a very good job of adapting. The difficulty comes when the situation changes. Despite finding new situations and new people, we generally tend to feel and behave as though we were still in the same situation with the same people. So, a Psychodynamic psychotherapist will spend some time helping you to understand the ways you adapted to your early life, and how those early experiences are affecting your current circumstances. Then they will help you to reconfigure your approach to the world so that it is more flexible, and more congruent with your current situation.
Those are the three major types of psychotherapists that you'll encounter in the wild. Of course, there are a wide variety of offshoot sects and in-betweener “eclectics” with whom your mileage may vary. The important thing is that you can personally like and respect the therapist, and feel liked and respected by them. It is also important that you enter into the therapeutic relationship with a good understanding of how your therapist will approach the treatment and why. In many cases they will offer you an explanation of how they work as a part of the early stage of therapy, but if they don't you should definitely ask.
This is because psychotherapy is a collaboration. There is no magic pill for the therapist to feed you to make you perfectly happy and well-adjusted, and there is nothing the the therapist can really do “to you” to make it happen either. It's going to take some work on your part. A good therapist will be able to help you to feel motivated to do that work to some extent, and to help you figure out exactly what types of things you need to do, but do not expect to enter into psychotherapy as a passive recipient of treatment. That's why it is so important for you to know what is going on in the therapy, to understand your therapist's theory of change: so that you have some idea of what you're expected to do if you're going to change yourself and your life for the better.