To add to Matt's reply, each theatre has a different, unique relationship with its stage manager. One theatre's standard practice could cause people at another theatre to tear their hair out. The new stage manager's job is to fit him- or herself to the theatre in as seamless a manner as possible.
I think the way to do that is to build up the trust you have with your co-workers. Interestingly, that trust is built just as much by how you handle your mistakes as it is built by all the times you make the right call. It strikes me that fear of taking any steps forward is pretty clear evidence of untrustworthiness in a stage manager.
There's a difference between the rehearsal phase of the project and the performance phase of the project. Speaking in the most general terms, and not knowing anything about your specific situation, I feel comfortable saying that SMs stay out of design or aesthetic decisions prior to opening. The most I think an SM can do is point out logistical or pragmatic consequences of particular artistic choices - for example, when a scenic designer I knew wanted to have the pre-set of our three-quarter thrust include a large elevator in the down position, leaving a large hole in the middle of the stage, I pointed out that audiences in that theatre often walk across the stage before ushers can catch them, and if there's a hole in the stage, how can we ensure their safety? I refrained from offering any of the three or four solutions I could think of off the top of my head, because that would interfere with the artistic process.
Once you are in performance, though, that changes. You have the example of the opening night as the artistic ideal each performance is striving to achieve. Variations from that ideal are easy to note, though sometimes harder to correct. Here is where the SM has more discretion, I think. In preparation for that role, I always pay very close attention to the director's work on the play and will sometimes ask for a face-to-face meeting with the director during the preview process to make sure that my eye is seeing and noting what she wants me to be watching for, and to strategize on how best to communicate notes to particular cast members.
hope this helps,