I tend to always shoot for business casual or better. Part of it is that I'm young, and often work with older casts/directors, etc, but part of it is that is what makes me feel good. I always joke that the two items of clothes that make me feel the most confident are my steel toes and suits. I'm personally a huge fan of the sneakers, nice jeans, and a button down look and a suit jacket if it's chilly. I almost always wear closed toe shoes for safety and practicality (the primary spaces I work in require a lot of walking through the scene shop to fetch extra chairs, props, etc, not to mention the usual issues of moving heavy things around), and heels are fairly uncommon for me. I find that I dress a little better for SM jobs outside my university just because those are times when I can dress specifically for the job rather than class, lighting calls, dance classes, etc, though I try to keep it all fairly consistent because I prefer to promote a professional attitude in the university setting. I've found it has actually helped maintain a better attitude in the rehearsal room among some of the less experienced members of casts. I think that it's most important to wear whatever it is that makes you feel confident, authoritative, and ready to run a rehearsal.