I have had 4 HSMs so far (junior house, main house, a change at sixth form) all were good experiences.
Setting the tone in house is important, as others have said a happy, supportive atmosphere between HSM, matron, residents and cleaning staff is key. We have always seen this.
Understanding the individual child and accepting their personality type. One of my children is a clever, polite, very conscientious introvert. Not a problem in the classroom but in house she is not one of the girls to volunteer for stuff, hug the other girls or join in much basically! Of course she had to do a certain amount of joining in but both her HSMs accepted her as a bookish type who did not enjoy for example a costume party etc (she would be asked to attend for 30 mins and then given the wink and allowed back to her dorm with a resident in house). They were very good with her. As parents this was really appreciated by us. Our son is very kind (but lazy and does the minimum to get by) and he was tasked with buddying up with and sharing a room with a new boy coming from a state school and supervising the youngest year group in his house. Not unusual jobs at all but his HSM knew where he would be helpful and my son really enjoyed these roles and I saw myself how the younger boys in house were fond of him.
Flexibility is important. Our son had a HSM who ran a tight ship, he was very good but inflexible. For example, it was almost impossible to get any wiggle room on taking our son out of school after games on Saturday if it was an ‘in weekend’.
Good humour, a HSM needs to be young at heart, enjoy the hustle and bustle of young people.
Zero tolerance to bullying, stamp it out quickly.
As I say our experiences were all good relationships, certainly didn’t come across any drinking!