Music, having background music the model likes is a must; the music helps
the model relax and get into the mood of modeling.

Music, as mentioned before is definitely a plus and does just what DreamCatcher says. I think that it's important to find a good mix of bring professional and having fun. Every model is different and has had different experiences, are more or less shy, etc. The photographer needs to be honest about what's going on, tell the model what is needed and be patient. Many newer models still need time to adjust and figure out some of the more common poses and what is expected of them. Confidence is infectious and tactfully letting the model know what they are doing well and what they need improvement in can be great in teaching them, if it's delivered correctly. I have found that some models have some pretty good ideas for projects and simply need someone who sees the project like they envision it. This being said, the model's job is primarily modeling, not directing, but a little give and take is ok in many cases.

Asking another photographer I know, he says that it has a lot to do with who you hire for a particular project. A model who is confident, has a lot of personality and who is experienced and willing to learn, taking the photographer's direction is going to do a great job compared to one who is timid, unsure of themselves and thinks they know everything (when they don't) is most likely only going to frustrate everyone working on the project. I would recommend that photographers meet their models and spend a bit of time with them, if possible. When they know them, they'll be able to direct their strengths and quickly identify and neutralize their weaknesses. A good model is in many ways like an actor. They should be able to convey a wide variety of "roles" through the camera in the same way that a good actor makes you not realize that they are acting and not the person being portrayed.