First of all the facilitator needs to be able to be present.
For a beginning facilitator that simply means that she must be able to stay in the same room with the client for an hour or two, without falling asleep, while maintaining some sort of interest in the client's situation. But that is only the low rung of a long scale of degrees of presence.
An advanced facilitator would have a presence that would be felt in the whole room. Clients would frequently get well simply by entering her space. She would permeate the space with confidence and certainty, and things would tend to sort themselves out without much effort on her part.
There are many steps in-between of course. Anything you can do to be more there with the person leads in the right direction. Becoming less dependent on the ritual of a session, being more perceptive of what the client is actually doing, clearing your own semantic reactions, practice, practice, practice.
Next, the facilitator must be able to be neutral and non-judgmental.
A new facilitator must at least be able to fake it and suspend her own attitudes and reactions while she is doing the session. She would exercise not having distracting body mannerisms, and she would exercise speaking in a neutral language.
An advanced process facilitator really would be non-judgmental. She would be perfectly willing to explore any viewpoint without any need to make it right or wrong. She would naturally see things from a level of wholeness and cause.
The facilitator can develop her ability to be neutral by doing communication exercises, by following the rules of processing, and by familiarizing herself with many different viewpoints.
Next, a process facilitator needs to be cause, and she needs to know what to do.
In the first place that just means that she needs to have a system of knowing what to do next. She might maintain index cards with directions on them, or develop mnemonic systems of remembering different techniques. As long as she maintains the appearance that she is in charge and she knows what she is doing.
A more advanced facilitator would more let her own creativity loose. She wouldn't need to refer to anything but would simply know what to do at all times. If she doesn't have an existing technique that fits the job she makes one up. The client probably won't even be aware that anything systematic and technical is going on.
The facilitator will become more and more cause as she makes the principles of processing her own and she starts to think with them. But really the key thing is that she takes responsibility for the session.
Next, a facilitator needs to be able to communicate. That includes the ability to say things in a way so that people receive it. And to listen to what people say and let then know that she heard it. And to make sure that questions are answered. These skills are also practiced in communication exercises.
For a starting facilitator we are simply interested in that she speaks so one can hear it and she gives some kind of signs to acknowledge that others have spoken.
An advanced facilitator might resolve something major simply with one well placed question or direction, or just with one good acknowledgment.
Finally a facilitator must be able to stay on a subject till it is completed. She should at least be able to stay on one subject for the duration of a session, and get back to it when necessary, despite she client getting off the subject.
Advanced facilitators would be able to juggle more actions at the same time and still get everything finished.
All of these abilities are basic human abilities: to be there, to talk, to listen, to understand, to act. An average human being can do these well enough to do a simple processing session. Which means that just about anybody can get started right away as a process facilitator. But from then on we aim at improving these skills to perfection.
A master process facilitator who produces miracles still does the same actions: she is there, she talks, she listens, she understands, and she acts. And she might well tell you that this is all that she does. But she does it to perfection.