Expectations: There seem to be overblown expectations of what HB is and what it can do. Some people expect that they'll be taken on a wild trip into the transpersonal realm of the human psyche, full of colourful images, meetings with God and answers to all questions. Others expect that one HB session will cure their addictions, neuroses or whatever problem they are dealing with. While all of this can happen, it is generally not the case. And it virtually never happens in the first session. My advice -- as someone that has "breathed" at HB sessions at least 20x (over the course of seven years) and that has assisted at several sessions as well -- would be to try to have no expectations and use the first session as a "getting-to-know altered states of consciousness" session. I also like the advice that it's good to experience at least 3 sessions before making up one's mind about HB, because each session is so different - all of my 20 sessions have certainly been different.
Session leader: This is probably the most important point and I can't stress this enough. Only attend and breathe at sessions that are lead by highly experienced pracitioners that have been certified by the Grof Transpersonal Training Program! There are too many people out there that attended a couple sessions and then began leading their own sessions. This is dangerous as these people are not trained to properly handle all of the situations that can occur. Officialy trained practioners are obligated to provide a 3-4 hour presentation about HB, which must be attended by all persons before they are allowed to "breathe" at a session. My advice would be to definitely attend this initial presentation and only proceed with attendance at the actual breathing session if you have a good feeling about the practitioner based on the initial presentation. And if no such initial presentation is offered, run far away! :-)
At the end of this post I would like to express my opinion that when lead by the right people, holotropic breathwork is a perfectly safe and wonderful method of self-discovery. It makes it possible to put aside our usual assumptions, habits, roles and social masks, explore our psyche, discover new parts of us and integrate these parts into our lives. This makes us more complete as human beings and in turn more happy, which brings to mind Carl Jung's famous quote: "strive not to be perfect, strive to be complete!"
For more information about Holotropic Breathwork, please visit its official website.