If you are pursuing a conservative industry and are in doubt, observe well dressed women in your industry on the job, at career fairs, at information sessions, etc. Skirt lengths come and go. Before choosing a skirt to wear, sit down in it facing a mirror. That's what your interviewer will see. Ask yourself whether it will be distracting or reinforce your image as a person who looks appropriate for a business environment or gathering.
Women generally have more options with suit color than men.
For example, while a women could look conservative in a slate blue or light gray suit, these colors would be inappropriate for men. Underneath the suit jacket, wear a tailored blouse in a color or small print that coordinates nicely with your suit. A fine gauge, good quality knit shell is also appropriate underneath your suit jacket. Jewelry and scarf styles come and go. Keep your choices simple and leaning toward conservative.