My best teacher “hung up his stopwatch” this year, but I still consider him both a mentor and a friend. We met when he was PSM for a production that brought me in during tech week as a second ASM. We went on to work together on 3 more shows and a workshop/staged reading, for two different theater companies.
What made him great, the important things he taught me, and what I try to pass on to other SMs are all the same, but hard to narrow down to just one: preparation, honesty, confidence, focus, grace under pressure, and positive attitude are all part of it. Some of these are traits that you can’t learn though anything other than experience. One skill that can be taught (to the willing!) is accuracy, which goes along with the Never Assume Anything principle.
Don’t give an actor, director, or anyone on the production team, incorrect information. “I don’t know” is an acceptable answer if it’s followed by “I will find out and tell you.” It’s better to say “let me check my book/ask the TD/look backstage” than to guess on an answer, and have someone plan around that guess, only to find out later that you were wrong, and time and effort were wasted because of that. At the very least, you can qualify an answer with “my understanding is that xxxxx, but I will confirm that (later/with the designer).”
That said, mistakes will be made. When they happen, don’t try to cover them up, don’t over-apologize, and don’t let the same mistakes happen again. Explain the situation without adding drama, adjectives, or accusations.