Although our culture has gotten much more casual since I've been speaking professionally and we don't spend as much time talking about dressing for the stage as we used to, I still think there are some basic rules which need to be observed.
1. The very first thing to remember when speaking is that the speaker needs to be wearing something just a tad dressier than the audience.
I was sitting in the audience of a group of young mothers of pre-schoolers and when the speaker came to the stage, I'm sure my mouth dropped open. She was a very good speaker and had awesome points, but the way she was dressed completely distracted me. She had on jeans--with holes in them (I know, I know. That is a very "with it" style for the younger generation.), a plaid shirt over a camisole, wrinkled, and flip-flops.
What a speaker wears lends credibility to what he/she is saying. This young gal could have easily worn jeans, but dress jeans would have been more approriate, and a camisole with a jean jacket would have looked sharp. And I don't mind sandals, if one has a fresh pedicure and the style is dressier than rubber flip-flops.
In a retreat setting, the speaker can fit it by dressing comfortably and casually, but even there, one needs to remember to tic it up just a notch.
2. Don't let current styles lead you to make foolish fashion faux pas. For example, short skirts are currently in style, but please not on stage. When an audience is looking up at one on stage, that short skirt gets even shorter and will make the audience uncomfortable. Anything that will distract from your message needs to be eliminated ... huge earrings, a skirt that is too thin and the light on stage is backlighting through your skirt, a slit in a skirt that is too high, a too-low neckline, stilettos that are too high.
3. Do dress according to your personality. If you are a bit flamboyant, wear your bright colors and your skirt with the fringe or bangles. If you are more classic, wear your elegant silk suit with a beautiful blouse. If you are more town and country, wear a casual suede or leather skirt or pants with some beautiful boots and a stunning silver and turquoise belt. People enjoy seeing a speaker's personality portrayed through their clothing.
Don't be a slave to fashion, but do use common sense when dressing for the stage. What you have to say is the most important thing. What you wear should accent and support your message.
My newest book, a compilation of four biblical fiction novellas, Hidden Faces: Portraits of Nameless Women in the Gospels, just released last month. Go to my web site at www.goldenkeyesparsons.com to order.