Men should typically wear a suit. Women should wear a suit or skirt and jacket. Clothes should be clean and neatly pressed. Shoes should be shined. You should evaluate the level of dress of your audience and dress one level up.
Pearls adds credibility.
Dangling jewelry is distracting. No audience wants to listen to an unenthusiastic, disinterested speaker. If you don't have a positive attitude about what you are talking about than why should your audience. There may be on occasion when a speaker should have something other than an upbeat attitude, but this is the exception and not the rule. Think happy thoughts.