I have only had the fortune to work with a hair stylist once so far which is a shame, good hair stylists seem harder to get than good muas.
Have some creative vision. They are the hair expert not me, I want to rely on them to tell me what will work best for my idea, the model and time available. If I have to try and articulate exactly what I *think* I want they could do that to the letter and it may not work for the shoot because I’m a photog not a hair expert. I run into this problem with MUAs often.
Know what is on trend with regards hair styles. I can’t always know, they are there because they are the expert.
Play nice with the mua over table space and working on the model
Be fast. Time is precious and hair can take a long time
Stay on set to keep the hair looking it’s best and pick stuff I may miss not sit in the corner txting/eating
In terms of knowledge technical aspects of the production not much. I think this is more important for a makeup artist since I feel they really should have some lighting knowledge so I can communicate this to them easily.